Fix homieiot#689: Use 6.11.x version of ArduinoJson

Various code optimizations (homieiot#647)

* Fix the ability to provide `null` for `wifi.password` for open WiFi networks

Additionally, this commit will now explicitly allow to omit `wifi.password`
from the configuration. Leaving it out will be treated as setting it to `null`.

* Make `ota.enabled` configuration optional

* OTA will be disabled by default if `ota.enabled` is not provided

* Avoid unnecessary copying in Config::getSafeConfigFile()

Merge branch 'develop' of https://github.com/homieiot/homie-esp8266 i…

…nto develop

Merge branch 'develop' of https://github.com/homieiot/homie-esp8266 i…

…nto develop

Update Readme - Homie Convention

📝 Update links to configurator

⬆️ Update dependency to "ESP Async WebServer" (homieiot#434)

🎨 Fix broken doc link in README

Bump to 1.5.0

Bump version