Fixed some bad exception logging in HttpUtil::get
* Discarded the LRUMapTileCache::TileRemovedListener as it's never used
* Removed < GINGERBREAD support from the LRUMapTileCache::remove method
* Added some comments to recycling ReusableBitmapDrawable instances - I'm pretty sure we *only* use ReusableBitmapDrawable instances
* Added more warning level logging to see what's going on with download errors in the TileDownloaderDelegate.
* Removed useless logging message when the SmartFSProvider fails to load anything.
* Threading has been simplified now so we don't have separate disk IO threads and network download IO threads.
* We just have IO threads as networking and caching is tightly coupled together within the SmartFSProvider.
* All threading is actually handled by an ExecutionService within the MapTileModuleProviderBase

So with that, we've removed NUMBER_OF_TILE_DOWNLOAD_THREADS and NUMBER_OF_TILE_FILESYSTEM_THREADS and consolidated that into NUMBER_OF_IO_THREADS.
Dropped MapTileFilesystemProvider as it's no longer used.