Apply correct body classes for block region emptiness

If the settings and/or navigation blocks were hidden using Decaf settings,
incorrect body classes were applied if this caused a region to become
empty.
Tidy up actionmenu styles on course/category manager

The course/category manager uses some action menus which were being
styled poorly, with alignment issues etc.
Tidy up white space.
Update readme shown in theme chooser
Version bump to 2.0 RC1