Public API update

Updated public API(see MCPELauncher-app commit of AndroidManifest.xml),
added some strings, cleaned preferences.xml, added a couple of bugs. ;)
Public API update part 2

Simplified HoverCar class, moved all API classes to subpackage, added
deprecation warning, removed unused imports, fixed ImportScriptActivity.
API Demo and MCPELauncher-app also were updated.