storage: add file update date to FileInfo.
Savestates and custom textures can be loaded from content path / ASS.
Cache last savestate update date to improve perf on android.
android: Don't use scoped storage for android < 5. Optimize listContent.
Fix getSubPath
android: instrumented storage test
introduce Storage abstraction interfaces
use Storage i/f to load zip and 7z archives, cdi/cue/gdi/chd media,
cheats and to find custom textures.
Use android file picker to add storage. Request persisted access perms.
jni helper classes.
Issue #813