hide _mqtt_client_secure under preprocessor check

- 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

* Rework MQTT sync client configuration

* MQTT_LIBRARY_...

* comments

* fix not doing any checks for bearssl, remove afterconnected template for mqttclient

* comments

* comments

* secure bool stub

* typos, always include sc helpers

* fix on_fingerprint return type

* typo

* typo

* indent

* tag is already in config obj

* generate mqtt featureset string at compile time

* reword again

* trusted_root_ca

* MQTT rewrite with SSL fixes

- Added Arduino MQTT library support (actively maintained)
- Added support for BearSSL (core >= 2.5)
- BearSSL validation: insecure, fingerprinting and CA validation
- AxTLS validation: insecure and fingerprinting
- Support MFLN in order to reduce heap usage

* Better header incl, fix building w/ no NTP_SUPPORT

* Clean up code, use DEBUG_MSG_P

* Fix compile error

- 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

* 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

- store system crash counter and reset reason in rtcmem instead of eeprom
- store relay state mask in rtc in addition to the eeprom
- store relay state in eeprom only when boot mode requires it
- simplify relay state mask calculation / reading using std::bitset
- light state save and restore
- energy total save and restore

https://github.com/xoseperez/espurna/issues/1465#issuecomment-484566975

This reverts commit 7ad0e3a02b.