* web: re-add wifi scan action, send as json array

* ws: forcibly inline send functions

- remove "platform" key, see #1440. this implicitly sets schema to "basic". pending some other clean-up regarding json and mqtt queueing, other schema can be added down the line 
- updated ws module queue elem to capture callbacks list, allows to pass more than one callback (for example, when they are generated on the fly as lambdas, see ha wsPost usage)
- modified method to send ha config to use global ws queue, fix #1762 problem with empty topics and ensure json allocation is consistent.
- use existing defines to set mqtt payload options. amend #1085, #1188, #1883 to use the set payload value. drop HOMEASSISTANT_PAYLOAD... defines. 
- update MQTT_STATUS_ONLINE/OFFLINE and RELAY_MQTT_ON/OFF with runtime configuration
- filter payload strings so that the resulting yaml value is not interpreted as bool (python True, False)
- helper method for settings to streamline string values manipulation

* clean-up ws declarations, remove old stubs

* always fw declare callback types

* wsPost is only possible with WEB_SUPPORT

* some more ws methods

Amend #1843 , since we have updated ESPAsyncWebServer
Fixes (again) #1300

Gather WS debug messages in a buffer and flush every N times
info,keys,crash actually output data now

- update every dynamicjsonbuffer with fixed size constructor argument
- change to ws callback registration to use a class builder (just cosmetic)
- test multiple ws data callbacks for each module
- remove some of the static strings in favour of ws data callback
- improve sensor ws callback data size, remove duplicated strings
- use static buffer in wsDebugSend
- postpone wsSend until loop, implement wsPost to allow other modules to queue message callbacks. remove Ticker based ws callbacks for data
- update WebUI files

* Configure WEB_REMOTE_DOMAIN at runtime

* typo

* MQTT: config change detection
* Reload settings when config json is uploaded
* Apply only new settings
* Finish config early when not enabled
* Reuse existing buffers from getSetting String using std::move

* Simply print timestamp for supported destinations
* Update ws destination to support 'prefix' sub-key
* Avoid void casting in telnet module

* send all ws config at once on start
* reduce ws json overhead by creating message buffer manually
* use k:[values] instead of k1:value1, k2:value2 etc. for lists

- Heartbeat mode and interval configuration added to WebUI ADMIN page
- New option HEARTBEAT_REPEAT_STATUS: on device startup full heartbeat information and after HEARTBEAT_INTERVAL only STATUS report.
- Enhanced first heartbeat message - on device startup it will send heartbeat after ntpSynced will be true to get device time.

P.S. Code is tested. Web part is not compiled, and not tested. I hope it will work :)

Add support for humidity correction