modchooser tiles: Visual fix for selected tile

Fixes #12
Action menus: position fix for inline folders

Inline folder resources' edit buttons were overlapping the folder name.
Persistent editing: fixes for course_section_cm_list_item

This function was spitting out warnings if $USER->editing was not defined
(such as when not logged in or using guest access).
Back to Top button: reinstate from non-responsive Decaf

This feature hadn't quite made it into the responsive Decaf.
Version bump to 2.0 stable