Combine all bookmark related buttons

[GoogleCodeExporter]

Currently, there are three buttons:
- The bookmarks button (introduced in Fx 4) to replace the bookmarks toolbar 
and the bookmarks menu. (Both are invisible in Fx 4 default setup)
- The bookmarks sidebar button (rarely used)
- The toggle button provided by Hide BookmarksBar

Hide BookmarksBar should integrate into the Fx 4 bookmarks button and combine 
all functionality in this button. There should be no equivalent button for 
pre-Fx 4, but it should still be compatible.

Hide BookmarksBar already integrates into the bookmarks button on Fx 4:
- In normal mode, it displays its hotkey
- In normal mode, the toggle command works with Hide BookmarksBar
- In hover mode, it removes the toggle command
- In hover mode, hovering the button shows the toolbar

It should also be possible to reach the extension's settings through the menu 
to implement all functionality of the extension's button.

In the menu, there should be a command to show the bookmarks sidebar to 
implement all functionality of the bookmarks sidebar button.

Original issue reported on code.google.com by [email protected] on 15 May 2011 at 5:51

• Blocking: Different icons for toolbar buttons #3
• Blocked on: Unknown behavior when the toolbar buttons are not in the toolbox #6