Profiles

Closes #40 (closed).

This implements all of #40 (closed) except that it doesn't allow Extended Interpolation of variables defined in profile config files, which also means that if you use Extended Interpolation on variables such as USE, you will get the local version, not the version containing the combined values from all config files. While this feature would be useful, it's not exactly simple to implement and I'd rather not spend too much time on profiles, given that we're not making that much use of them anyway.

Note that this breaks things, as some function import paths changed due to me moving the openmw config file functions to a new module. For all of these, I ensured that they can now be imported directly from the portmod module so that we can more easily support them in future.