Android Mapsforge 0.4 port

Ported the Android App to MapsForge 0.4 (rescue branch).

The jars have been taken from the Mapsforge Jenkins instance.
This PR also contains two other bugfixes:
a) The Downloader class now uses a GET instead of a POST request, because the download server doesn't answer the POST request correctly (which resulted in failed downloads)
b) The app diddn't run on devices with SDK Version >= 19, because of an invalid MEDIA_MOUNTED check, which was corrected.