Revert removal of setcss for repeat groups.
Fix bug stopping validation

Calc and CCD were overriding attachToForm - and icons were not being
set. This fix effectively does a call parent to set the icons.

In addition:
1.  a fix that was preventing success messages being shown more than
once, and
2. improved ajax calling using all Request callback functions
appropriately and handling errors better.
Improve ajax error handling

Improve ajax error handling by using all mootools Request callback
functions appropriately.