Add support for HTTP OTA updates

[zen]

Sensor should be able to request new firmware through HTTP OTA procedure.
There should be pre- and post-update actions, specifically turn off the heater.
Sensor should send following data to the server:

• hw_version
• sw_version
• devel (tree or false) - for development type of firmware

Server will decide if there is a new firmware based on hw_version (denoting firmware line) and sw_version (using semver naming).

[zen]

https://github.com/platformio/framework-arduinoespressif8266/blob/master/doc/ota_updates/readme.md