general structure for mb tiles
tiles from local db working
added javadoc, some refactoring
added switch in settings, fixed caching issues
fixed some more caching issues
changed mb tiles db origin resource from assets to sd card
added file selection dialog to select mbtiles db file
improved db opening/closing according to mapworker queue
not final implementation of multiple sources selection
background source selection completed
Merge pull request #21 from RoProducts/mbtiles

Mbtiles from local database