Edited datatypes.py and admin.py

datatypes.py

- removed department and workload Properties from the Module model, as they are not really needed in the app

admin.py

- added a handler for a new function, IndexModule.
   Calling this function (preferably from a cron job) causes the server to request NUS Modules via the IVLE LAPI for an entire semester (takes ~300+ seconds), and stores them in the database, using the Module model declared in datatypes.py