ref. #2423

amend c100696f7b

- retain setting
- generate topic and message in the discovery object instead of
creating them all at once
- re-implement relays, lights and sensors discovery
- rework name normalization, use relative magnitude indexes
- replace original lights code with schema: json, subscribe to a special
topic to handle lights instead of using the common API
(still wip - colors, hs, temperature settings)

resolve #630
resolve #1564
resolve #2403

- simply use a basic {String, String} struct
- fix MQTT_TOPIC_TIME vs. MQTT_TOPIC_DATETIME
- get rid of unused chaining and indexes

- shrink utils source file, move heartbeat and boot management into system
- improvise with 'heartbeat' functionality. include scheduler implementation that will
manage the per-module heartbeat callbacks with individual 'mode' and
'interval' settings. current ones are mqtt (including relays, lights, thermostat), debug and
influxdb. preserve heartbeat NONE, ONCE and REPEAT, REPEAT_STATUS is effectively a hbReport & status bit.
- mqtt heartbeat is managed through mqttHeartbeat() callbacks
- tweak mqtt callbacks to use lists instead of the vector, slighly reducing the size of the .bin
- update WebUI, include report setting and update hbMode values
- make sure general.h settings include new heartbeat,
move constant definitions outside of the header
- correctly include dependencies through the .cpp, avoid leaking
internal details.
- as a side-effect, base headers are no longer included recursively

- for some reason old key was default-constructible
- fix magnitude key generation

- specialize ntp functions to split time_t into 32bit ints when time_t is larger than rpn_int
- rework 'tick' variable into an operator that can be triggered once
- make sure operators expect new time_t split via argc of 2

- make sure server is never empty
- disable dhcp option when server *is* empty
- update configure() to detect both tz and server changes

- allow strings in mode (off, on, none)
- fixup type used for the mode to be am enum instead of int
  (todo: allow webui to accept strings?)
- some cli updates using new funcs

update custom action callback to also get the event
buttons fan actions
ifan buttons are handled through action instead of manually
fan settings and api are (sort-of) generic

resolve #2416

update to terser v5
replace gulp-remove-code with a rough equivalent in the gulpscript itself
replace gulp-inline with gulp-inline-source-html
remove base64 modules as redundant when running inline-source (does both)
remove crass as redundant when running inline-source (uses csso)
fixup jquery source map comment (but still keep the actual file)

at least now this seems stable enough to start more of the ui tweaking

pure-css 1.0.0 -> 2.0.3
datatable 1.10.16 -> 1.10.23
generic jquery-slim -> custom jquery/jquery@a32cf6324f8f2190e66a687e94be9687ebf840b7 slim build with an addition of -sizzle

does not seem to be breaking anything (yet)

note that this does not show the correct error line b/c we filter this
through the remover() first

ref. https://github.com/xoseperez/espurna/issues/1132#issuecomment-431868924
it is slightly bigger, but better looking and no jquery dependency

rework colorpicker style as well, hide to prevent sending garbage when
lights are off. update lights module to send `lightState()` and separate
state from status payloads

yes, input[type="color"] is an option, but it does not look good

support es6 syntax
use js comment style in custom.js
only minify the custom.js

using 4.x branch, since 5.x wants async / await and more changes to the gulp script

- gpio module now tracks the known providers (right now, hardware and mcp expander)
- refactored relay struct to use 'Provider' implementing setup,notify,change,boot instead of just BasePin actions
- refactored button module to use gpio provider instead of referencing types itself
- removed dual & stm code from buttons, migrate both to relay module
- added status notify and change callbacks for relayStatus (i.e. 'notify' when relay status was called, but not changed. and 'changed' when it did)  
- relays runtime configuration keys
- relay command now shows configured relays and current & target statuses
- refactor the code using relayStatus(0, blah) under LIGHT_PROVIDER check to use lightState instead
- remove rfbridge code form relay module. implement through a basic state listener in the rfbridge module, depend on RELAY_SUPPORT
- allow to bind rf codes to real relays
- drop tuya-specific lights provider, remove tuya code from relays and lights modules
- integrate tuya via relay listeners and providers, use lights custom provider
- implement channel transitions for tuya. disabled by default, and transition time and step are overridden to 2000 + 100. needs to be set to some value below the total time (i.e. `total transition time / step time == number of steps`, we need to figure out a correct time that serial comms could handle)
- lights custom provider (global, not per-pin) and state listeners
- remove lights code from relay module. implement through providers & listeners in the lights module, depend on RELAY_SUPPORT
- lights per-channel relay provider (unused atm), depend on RELAY_SUPPORT
- refactored channel transition - calculate step only once, make sure time + step values are sane, generate quick transitions with very small delay (10ms hardcoded) for transitions during OFF state i.e. we no longer waste 500ms (or whatever transition time is set to) on boot doing nothing
- transition time + step parameter for the lightUpdate
- report mask parameter for the lightUpdate
- minor fixes across the board

resolve #2222

- Update README.md - add garland description
- Add new animation - Dolphins