Set callback for bookmark gengrid item instead of items thumbnail.
[Issue#] https://bugs.tizen.org/jira/browse/TT-135
[Problem] Clicking on bookmark folder text doesn't work.
[Cause] Callback was set on thumbnail instead of on whole item.
[Sollution] Move callback to bookmark gengrid item click.
[Verify] 1. Run browser
2. Create some bookmark folders
3. Open More Menu -> Bookmark manager
4. Click on some bookmark folder description
5. Bookmark folder shold be opened.
Additional changes:
- Changed some function names to make code more self-explaining.
- Removed redundant focus managment callbacks causing problems
in the current approach.
Change-Id: Ibddc457a7cfdc19f7b68ce4163f4b2ae04d793db