Added main menu & PreferencesActivity
Added BootReceiver (still in progress)
Simpler Intent construction call
Fix security issue when using *printf functions and the format string is not a string literal.
Remove duplicate struct definition that is already defined in the NDK headers
Moved native code to jni/

* Renamed gogoc-android/native/ to jni/ under toplevel
* Moved gogoc-android/jni/Application.mk to jni/, and updated
  APP_PROJECT_PATH accordingly