Reinstall flask-compress.

This was removed during the major restructuring of
the application.
Initialize and use the compress object in the app.
Set config variables as needed.

Fix the try/catch statement by using python's
dict.get() method.
Removed old code in user models file; Refactored obtain_class_list method
Merge pull request #266 from CalPolyIEEE/gzip-responses

Compress responses using Gzip.