Started testing the hardware. Need another On/Off-controller since the current model allows only 2 seconds time frame for the feedback from microcontroller and the SAMD21 with Arduino bootloader needs ~2.5 seconds for booting and setting the GPIO to High.

 Following initial tests passed (tested with example codes)

 - RFM95 module

 - I2C RTC (fixed a mistake in routing of I2C. SDA and SCL were swaped :(  )

 - uSD-card

 - LiPo charger

 - programming over USB

Next steps:
- order some missing parts (capacitors for the display)
- test display :-)