added parent activity to MainActivity. Back buttuon in upper left corner is now working.
Closes #78

* Major bug fixes concerning the connection with bluetooth devices. Added 30 sec timeout on connection in both device list and add device screen. Not finished with adding with QR.
*#78. I think this is closed as I havent encountered this problem after the above was fixed.
Further bugfixing

* Closes #78. I have never ecountered that the connected device is unselected in device list.
* Fixes concerning connection with QR-code. The device name and mac address is now stored properly and the connection works.
* The android device no longer need pairing with the arduino.
Merge branch 'bugfixing'