update : introduce double buffered event handling.

Signed-off-by: Kim <Kulling>
bugfix : fix some null pointer dereferenings.

Signed-off-by: Kim <Kulling>
- update : prepare taskgroup.
- bugfix : fix rotation in the class App::TrackBall.

Signed-off-by: Kim <Kulling>
- feature : add class String for a ce-specific string implementation.
- feature : add a string hash function.
- feature : add a unittest for the String class.

Signed-off-by: Kim <Kulling>