Fix problems with FormsetDataTable display

* display errors as tooltips, so that they don't stretch the table,
* make sure the "Add row" button is always displayed when the formset
  was created with extra>0
* don't delete extra empty rows from the end when the table when it is
  being redisplayed with errors
* make sure that only the "add row" button is clickable, not whole
  footer
* make sure the fields with errors are displayed as red

Change-Id: I7202965ba59f3565d350462c833d604782f7cc70
Merge "Fix problems with FormsetDataTable display"