fix gwt: 'join' in PausableThread
refactor: PbfTileDataSource -> UrlTileDataSource
cleanup
use LwHttp.Buffer to set limit on InputStream
settings: export slf4j
refactor: add TileLayer.initLoader()

- need to initialize worker thread after (super) class is constructed
add ITileDataSink.setTileImage(bitmap) to interface
fix: always initialize TileManager
add isValid() to Bitmap interface
simplify UrlTileDataSource initialization
new BitmapTileLayer implementation
Merge branch 'unify_tilesources'

- use same TileSource code for Vector- and Bitmap-Tiles
- update android-app