wip/ostbuild-v2 branch pushed to master, working on deploying

[Colin Walters <walters verbum org>]

I've been working on an "wip/ostbuild-v2" branch with the primary goal
of implementing a sane workflow for developers:

https://live.gnome.org/OSTree/Ostbuild/DeveloperWorkflow

While working on this though, I got tired of waiting ~10 seconds after
each build to re-checksum the target filesystem tree, so I implemented
an optimization that required breaking the repository format. 

I don't think the current developer workflow is anywhere close to
perfect.  In particular:

0) Having to edit a large JSON file to point to local sources is
   really crappy.
1) JsonDB is weird.  I'm not happy with it, but better ideas aren't
   coming to me yet.
2) The pull-components command is also unfortunate.  Ideally ostree-pull
   would download the metadata for associated components, but doing
   that is a layering violation (ostbuild depends-on ostree, but ostree
   doesn't depend-on ostbuild).

There's no sense in having the branch outstanding for long, and since
it's mostly there, I just went ahead and pushed.  This weekend I'll
work on moving the current ostree.gnome.org repo to a lookaside
and doing a rebuild.