Revert "(Android) Set rate control delta to 0.0010 by default"

0.01 is way too much for a default setting. 0.005 is already pushing it.
Redirect some defaults to g_defaults instead of "" string.
Actually read back RetroArch config.

onDestroy() is never called for some unknown reason, probably exit() in
NDK. Even so, finish() from UI thread via JNI doesn't work either <_<.
Merge pull request #773 from libretro/android-fixes

Android fixes