Comment updates to LRUMapTileCache and ExpirableBitmapDrawable
Added tests and code to serialize tile to File objects.
Added code to write SerializableTile objects to disk in parallel with
standard Tile, etag and cache-control objects.
* Renamed OpenStreetMapTileProviderConstants to OSMConstants
* Removed OSMConstants and IFileSystemProvider as interfaces that TileWriter implements
* Deleted IFileSystemProvider as it's only implementation is TileWriter and the interface type is never actually used.
Renamed the TileWriter to TileIOFacade.
Full stack traces only show up in logs if we're in a debug build now.
* ITileSource::getDrawable() now expects byte[] instead of a File object
* added a MERGED_FILE_EXT constant to OSMConstants for the etag/cache-control/bitmap merged tile fileformat
* SerializableTile no longer tries to use UTF-8 encoding for headers and just writes out raw bytes.
* A cache-control header is always saved with current time + 300 seconds on saveFile() invocation.
* SmartFSProvider now uses the merged tile format exclusively and does not use .etag, .cache_control or .tile files
* A successful HTTP 304 conditional GET will update the cache-control header inside the SerializableTile on disk
* BitmapTileSourceBase has been adjusted to load from byteArrays, but will still honour bitmap options