Allow pages in AdminMenu

[Gilbertdelyon]

I am adding some custom pages with tutorials/memos and other useful items for site administration and I realize the followings.

For a new page we can select : Main menu Item, User Account Menu, No menu, Footer, People.
it would be nice to also have Admin Menu

As well for Snippets:
Would be nice to be able to add a snippet in Admin Sidebar

Of course we can add items in the main menu, only for admin, but it's not very convenient when the main menu becomes too crowdy.

[luke-]

Snippets are not possible yet, since there is no sidebar. But the AdminMenu should be no big deal.

[Gilbertdelyon]

@luke-

AdminMenu should be no big deal

Would be perfect,
Thanks in advance,