Enhance Python unpacker

- ~~Set environment variable ANDROID_SDK to current SDK level (Build.VERSION.SDK_INT)~~
- ~~Check which libraries should actually be loaded~~ (See comment below)
- ~~Adapt sdl_main.c before creating the P4A distribution (= add step(s) in tribler-prototype/build.sh before distribute.sh is executed)~~
- ~~Integrate python and android parts into one APK~~
- ~~Adjust service text in notification bar (from android code)~~
- ~~Add info text under progress bar~~
- Don't load the main GUI before XML-RPC has a connection to Tribler (not really necessary)