bug 2293: better validation in overdue rules editor

bug 2293: better validation in overdue rules editor

If a rule should not be saved because a delay is
given but no letter or debar action is specified
for that delay, an error message is now reported.

Also:

* use "dialog alert" CSS class for confirmation
  that form was saved
* if form input is saved, retrieve the settings from the
  database again when displaying the form - this will
  help turn up any bugs where the script is not
  saving the overdue rules correctly.
* fix display of patron category in error messages

Signed-off-by: Joshua Ferraro <jmf@liblime.com>