Improvements to Custom HTTP Error Pages

- Added 500 Internal Server Error custom error page
- Added extra information to error pages for diagnostic purposes
- Migrated 401 and 403 page to separate instance Velocity model instead
of singleton (done to other pages earlier)
Modifications to Registration Editing Interface

- Registration editing interface now uses editable tables with AJAX
requests to provide an easier registration editing interface while
maintaining the more "powerful" editing interface through individual EID
requests
- Fixed a bug in the editing that prevented the cost from being updated
upon change to registration data
- If price of tests is changed in Admin Panel, the costs in datastore
will NOT update accordingly, this bug should be addressed in a later
commit
Added Messages to Error Responses

Errors are accompanied by an error message to be displayed on custom
error page
Minor Edit and Bugfix

- Empty aliases field in description list displayed on logon causes
Bootstrap to move up dd elements, fixed by removing empty descriptions
in servlet
- Added back edit radio buttons since entity keys can be very long, i.e.
removed unnecessary user action requirements