Upgrade django-wiki to most current PyPI version

We made 4 changes into our fork:

https://github.com/edx/django-wiki/pull/1 : was definitely fixed upstream (discussed in the PR comments)

https://github.com/edx/django-wiki/pull/2 & https://github.com/edx/django-wiki/pull/3 were the same PRs (against different branches) using ugettext_lazy rather than gettext for translations. Upstream does **not** use this. So we need to figure out if we need the lazy translations, and why.

https://github.com/edx/django-wiki/pull/4 is not present upstream but I think worthy of submitting an upstream PR.

So overall it looks like perhaps we can't use the Py PI version of wiki until at least the fix from PR 4 is present upstream.

So, I updated the django-wiki fork instead, given that we want the changes introduced in the 3rd and 4th PR to the repo.

Here is my method: I reset edx/django-wiki master to upstream master. I then made a new branch, https://github.com/edx/django-wiki/tree/rc/2014-11-21, off of the old release branch (https://github.com/edx/django-wiki/tree/edx_release) and then rebased it atop edx/django-wiki master.

Doing a compare, you can see that the rc/2014-11-21 branch contains the django-wiki master branch plus two commits: https://github.com/edx/django-wiki/compare/edx:master...rc/2014-11-21

I think this is the safer way to go, until we can submit patches upstream. We should do manual testing and try to merge this as soon as possible.