resolve #2327, #2220

- remove legacy support in the webui
- format datetime strings on the device, use NTP panel to display them both
- migrate from the old ntpOffset + ntpDST + ntpRegion to ntpTZ

* broker: declare and define per module

We no longer need to specify each Broker type in broker.h
But, we exchange that bit for explicit initialization of the instance

Define helper macros to generate boilerplate code
- namespace with Instance, Register(), Publish()
- forward Register(...) -> Instance.Register(...),
  Publish(...) -> Instance.Publish(...)

* don't check for broker when deps enable it

- general conversion from .ino modules into a separate .cpp files
- clean-up internal headers, place libraries into .h. guard .cpp with _SUPPORT flags 
- fix some instances of shared variables instead of public methods
- tweak build system to still build a single source file via os environment variable ESPURNA_BUILD_SINGLE_SOURCE

- Domoticz only accepts svalue <pressure>;<forecast>,
  failing to display anything otherwise.
  We don't have any forecast calculation (yet?), simply send dummy value.
- Move Domoticz code outside of sensor.ino

* ntp: try using sntp app from lwip, drop ntpclientlib

* fix display

* thermostat: fix day and month getters

* test build sizes with scheduler

* use system timers for once-a-minute scheduling, no polling

* tick

* avoid timestamps, use tm

* drop utc rpn operator, add utc_hour and utc_dow

* try to build with old implementation too

* dep

* notify ws

* progmem

* cleanup types

* offset tm values by 1 to match existing schedules

* avoid using ntpclientlib with rpn

* test. show debug strings in sch

* fix secureclient

* consts, fix unsyncing when changing tz (and not triggering sntp after reinit for some reason)

* startup time in seconds

* same delay as lwip

* header

* assume build timestamp is unixtime

* cache server value

* fmt

* typo

* handle dhcp request

* rename

* web

* TZ.h

* add notice about what alias means

* fix disabling NTP_SUPPORT

* scheduled ticker

* same behaviour as old module

* rollback rpn dependency check, utc_ prefixes

* ...

* comments, refactor naming