dep: add pygrader dependencies as submodules

dep: add pygrader dependencies as submodules

With the submodules checked out, you can run:

  $ PYTHONPATH=dep ./bin/pg.py ...

to run pygrader without installing any external pacakges on your
system.  With Gentoo's Python 3.3 support still flaky [1,2], this is
less painful than maintaining the dependencies by hand.

Checkout updated submodules with:

  $ git submodule update --init

The jinja2 repository is my local branch, which applies 2to3 directly
to the source (because we are loading jinja2 directly from the
submodule source).  I will rebase my jinja2 branch against new
upstream versions, so don't do any Jinja development based on my
branch.

[1]: https://bugs.gentoo.org/show_bug.cgi?id=437322
[2]: https://bugs.gentoo.org/show_bug.cgi?id=364877