wip-refactor-emacs-ui and Hydra interface

[Alex Kost]

Hello, I have pushed 'wip-refactor-emacs-ui' branch which contains emacs
interface for displaying Hydra builds and jobsets.  This 'list'/'info'
interface is absolutely the same as the one for displaying packages and
generations.

The most part of the branch is a step-by-step generalizing of the
list/info interface code, so that any type of data could be displayed
using it.  The changes are huge but mostly internal, though some user
variables were renamed/replaced (I'll mention the changes later).

So if someone wish to try this branch, the following new commands are
available:

M-x guix-hydra-latest-builds  (with C-u you'll be prompted for many things)
M-x guix-hydra-queued-builds
M-x guix-hydra-jobsets

Also you can press "B" key in a package list buffer to display latest
builds for the current package.

The branch is almost ready, only documentation and a couple of internal
things left.

A screenshot made several days ago: http://i.imgur.com/BvhHlkS.png

P.S.  Remember that Hydra is slow and Emacs is single-threaded, so a
synchronous process of receiving data from Hydra may "freeze" your Emacs
(can be break with "C-g" of course) for some time (especially for
complicated queries).

-- 
Alex