Replace classmethod's with module-level functions

[seanh]

In many places we have @classmethods where simple module-level functions would do (and would be more idiomatic in Python), e.g. the get() classmethods in the model/ classes.

Doing it with module functions lets us type module.function() instead of module.Class.method().

In many cases we're importing classes directly with from module import Class and then doing Class.method(), but from module import foo is bad style: ​http://docs.python.org/dev/howto/doanddont.html