Brownju/bug/47

Added a module for validating user input, moved the location of orvsd_central.database.Model to orvsd_central.models.Model, and added tests to general.register() which the function itself still needs to be tested for correctness.
I know I was talking about modularizing our utils file before, but that should be a separate bug. Instead, just put all of the validation stuff in utils.py.