Empty Admin menus are confusing

[bharat]

In alpha 4, we created Admin > Statistics and Admin > Content menus. But without Akismet, the Statistics menu is empty so for beta 1 we now create Statistics inside the Akismet module.

And if you don't have the comment, watermark and tag modules installed, the Admin > Content menu is empty so that's confusing for users too.

We should either inject a "this menu intentionally left blank" item for empty submenus, or we should hide empty menus. Pros of an "intentionally blank" placeholder is that it lets module devs know where they can hook in. Cons are that it confuses users to have extra useless menus.

[tnalmdal]

Fixed with: http://bit.ly/LHjYU and http://bit.ly/ffVg4
Moved the creation of the Settings menu back to gallery_menu::admin.
After the root menu has been created and populated, scan the menu looking for empty elements and remove them.