FaceGenManager and Species

# Description:
Based on feedback from my initial attempt at this in PR #2411 I'm resubmitting it without the JSON stuff and based purely on reading what directories and files there are.

This keeps the benefits of using the `FaceGenManager` and up front loading of the various images but it should be easier for people to add new items.

There is one continuing restriction imposed by doing it this way though:
* There must be an equal number of each type of gender specific item, i.e: 21 male hairstyles & 21 female hairstyles.

I've also added the possibility to have other *species*, this was requested on the SSC forums a long while ago in the form of wanting robots which would seem best to add as a separate species. We might never used it in Pioneer itself, but it might be desirable for a mod or a future fork.

# Notes:
I have no idea how to use the string formatting methods we seem to have so there's loads of hacky `snprintf` type shit. Suggestions for better ways to do it would be appreciated.

Also with SDL2 #2433 coming along shortly it might be best to wait for that and then fix this PR up with the necessary changes rather than muddy its waters.

Andy