Allow components whose XML manifests are without submenus to be selected

[roland-d]

Summary of Changes

Since a while now we can create back-end menus. This works for most components but not all. When you have a component which has no submenus in the manifest XML, this component won't show up.

This change will also make these components available that don't have a submenu entry in their manifest xml.

Testing Instructions

1. Go to Menus -> Manage
2. Filter the list on Administrator
   
3. Click on New
4. Create a new menu like this. Make sure the client is set to Administrator
   
5. Click on Save & Close
6. The new menu appears in the list now
7. Click on the title My Menu
8. You are now taken to the Menu Items list which is empty for this menu
9. Click on New
10. Click on Select behind Menu Item Type
    
11. In the list there is no option to choose the Multilangual Associations component. So we can't create a link to this component.
12. Apply the patch
13. Reload the page
14. Click on Select behind Menu Item Type
15. Now you will see the Multilangual Associations component in the list
    

Expected result

All installed components are shown to be selected

Actual result

Some components are missing and cannot be selected

Documentation Changes Required

None

[ghost]

without PR its possible to select "Multilangual Associations" or similar Components.

[roland-d]

@franz-wohlkoenig You are correct. I didn't realize until you posted that the test site I was working on is not yet Joomla 3.8.x. Apologies :)