About Us Window + Other fixes

Summary of Pull Request
New:
1. About Us Window added. Application does not crash when About Us selected from Dock->Tomboy->About Us
Fixes:
1. Toolbar now remembers the old configuration (It remembers what all items were added, and adds them accordingly in the next start up)
2. Adds the NoteBook heading in Note Dashboard
3. Adds Labels for Zoom Indication