MDL-39814 frontend: improvements to course/block editing
MDL-39814 frontend: further improvement to editing display
MDL-39814 frontend: improved display of activities when menu is displayed
MDL-39814 frontend: introduced an action_menu_action class
MDL-39814 frontend: increased size of editing icons for activities
MDL-39814 frontend: redeveloped overlay to correct tab-flow
MDL-39814 frontend: fixed zindex issue + spinner placement