TizenRefApp-8433 [Gallery] Implement event and caching mechanism in Model

TizenRefApp-8433 [Gallery] Implement event and caching mechanism in Model

- IMediaAlbum and Gallery interfaces extended. Reimplemented GalleryAlbum
  to cache MediaItems instead of requesting from DB each time;
- Fixed bux when transtion finished was not called from Naviframe in some
  cases;
- ucl::Event invoke() method renamed to dispatch();
- ucl::Event dispatch() method logic changed to not dispatch to a newly
  registered handlers while handling current event.

Change-Id: Ic8c99c4baca33aff104bbf221194207752677cbd