Refactored rooms, users to use prototypes; general simplifications

Rooms and users used to use a module pattern wherein I did data hiding, but I think
that made the implementation more difficult to read and a bit less efficient. Both
now rely on prototypal inheritance.

This commit also includes some other simplifications I made while refactoring.
Renamed files for simplicity

Both files are in the models/ directory, so I think having it in the filename is a
little redundant.
Removed server-side dependency on lodash/underscore
Standardized on single quotes in use strict statements