Changelog v0.6.9

* improved MqTT
* fix WiFi hostname during boot up
* improved login: only one session at the same time is possible
* fix UI: login screen for small displays; burger menu height; small modifications for import button (in setup)
* improved WiFi reconnect
* optimized performance: browser caching was improved to reduce requests from ESP
* improved NRF24 communication for more stable data transmission
* added / fixed MqTT subscription `ctrl/power/[IV-ID]`
* improved save settings
* improved UI in setup: now `.` and `,` are allowed as floating point seperator
* fix zero yield day functionality
* LEDs are now configurable to show if 1st inverter is available and if MqTT is connected
* LED are configurable to active high or low