set different cache dir for pbmap and oscimap.
show the max value of cache in cache size seek bar.
rewrite the reduce cache size methode.
cache: make db commits and dir scanning async
Merge branch 'release_0_4_cache' of git@city.informatik.uni-bremen.de:OpenScienceMap.git into release_0_4

Conflicts:
	VectorTileMap/src/org/oscim/cache/CacheFileManager.java
async cache management