Fixed a bug and added some TODOs.

MainActivity: enable Buttons on onResume()
MapActivity: Added TODOs
ServerRequest: reverted Tunnel1337's changes in the ServerRequest class
because it was buggy.

Tunnel1337:
- add a null check in 222 (got a NullPointer exception at the first
start)
- I always experienced never ending requests, please investigate this
- please test your commits extensively