MDL-31830 course: moved management ajax to dedicated folder
MDL-41394 course: management css is now in themes
MDL-41416 course management: converted category actions to action_menu component
MDL-31830 course: fixed management ajax config bug
MDL-41432 output: several action_menu improvements

The following improvements have been made:
* Items no longer MUST have an icon, it can now be null instead.
* You can specify the icon displayed to toggle the dropdown menu.
* You can add text in front of the aforementioned icon.
MDL-41416 course management: converted listing actions to action_menu's