Refactored code base:
* Code moved to additional modules each with its individual responsibilities
* Display module is responsible for input/output on the LCD screen
* wifihandler is responsible for handling WIFI connection
* Battey module is responsilbe to monitor the battery
* Data exchange should only be done via public API
Added WIFI configuration menu
* WIFI no longer specified via defines
* In settings tab, wifi submenu added to enter credentials
* wifi credentials are stored in flash after a successful connection
