Error on empty form fields

This addresses issue #284.  Some forms were raising exceptions when the input was blank.

This was caused by using "get" on form fields, which apparently return None without a default value.  

Changes:
* By entering a default of empty string (""), the problem was solved.
* In addition, I've implemented a number of browser-based tests.
* In implementing these tests, I noticed that only one form used a different (non-standard) class to indicate errors.  No extra CSS was being used to decorate these errors, so I migrated them to the standard class.

Testing:
* Manual testing of all forms for errors
* Implemented browser-based tests for all forms, for submitting empty forms.