implemented more meaningful display name generator

Before, if a display name is not provided we give the user a random
string as their display name. To make it more meaningful, I have
created a display name generator that appends the user's system role,
first name (if given), and a 4 digit number.

I have also removed the creation of dictionary from the import
algorithm, because it is not needed.
added new Criteria attribute

I added the default attribute to the model to let us know whether
the user wants to use it again in another course or just for the
current course. This idea came from a discussion about the possibility
of a user being overwhelmed with criteria, if every criteria they
have ever created is returned.