Adds a repostiory scene.

Repos are not yet loaded and there’s no way to carry the selected user
forward to load/fetch the repos.
Adds a model controller.
Implements Maybe.
Implements some generic functions over monads.
Maybe has a simpler block type.
Implements pipeline and lift functions.
Nothing can wrap an error.
Convenience for creating Maybes from common ObjC idioms.
RXPromise is a monad, although I’m not too certain of +unit: just yet.
Corrects the Maybe types.
Adds a convenience for boolean/error Maybes.
Monad fussing, notably adding recursion.

I don’t know how well-founded this is, but it looks pretty nice.
Persisting is a promise.

We’re propagating error state forward, but not all the way to the
client yet.
Forgot a fussed type.
Also forgot to add the monads to the project.
Persistence seems to be working now.

- RXPromise is now a class and not a protocol, basically just renaming
RXPromiseResolver
- persisting changes unpacks the inner Maybes and so forth (although
this still seems a bit ad hoc)
- adds a resource controller
- adds static API stuff to load resources from disk
Moves the add user button over.
Promises can be made with URL requests.
Resources can be loaded from the filesystem correctly.
Adds a users controller.