Simplifying the BAboutMenuItem and adding it properly to the locale kit's DoCatalogs list.

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@40967 a95241bf-73f2-0310-859d-f6bbb57e9c96

Introducing BAboutMenuItem.

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@40956 a95241bf-73f2-0310-859d-f6bbb57e9c96