Usage changes, fixes for selection handles.

Usage changes, fixes for selection handles.

- Introduce  `use_handles` boolean property that uses is_desktop like use_bubble instead of using
 ` use_bubble` for handles.
- Change Images to differentiate the cursor handle from the selection handles.
- Manage proper positioning of handles, improve movement using handles.
- Make sure handles are visible only when needed and are removed when TextInput looses focus

Test apk https://docs.google.com/file/d/0B1WO07-OL50_OFJHNVgyTFptQUE/