Make config download maintainable

Config download was incorrect* and confusing (pretty sure it ended up incorrect because it was confusing).

 - removed incorrect behaviour (was incorrectly using project type 'podir' for gettext projects in all configs)
 - changed the API for config generation so it is clear at every stage what type of config is being requested.
 - decomposed config generation so the basic structure is easy to follow.

* https://bugzilla.redhat.com/show_bug.cgi?id=959834