R1:8ce5dd31f63c

Show open Differential revisions in Diffusion browse views

Summary:
Still some rough edges, but this adds a table of open revisions to Diffusion.
See T262.

I'll make this a little better (e.g., "see all.." instead of arbitrary 10 cap,
or maybe move to top-level nav?) but I think I have to refactor some other stuff
first. This should let us root out any major issues, at least.

NOTE: You must associate Arcanist Projects with Repositories (in Repositories ->
Arcanist Projects -> Edit) for this to work!