Convert issue & thesis text from markdown to HTML on the server for SEO.
Clicking on a vote from a user's profile page takes you to a page with
the issue in the version it was at when the user voted, and with its
theses in the versions they were at when the user voted. Also changed
the History page to use the same 'show_version' template that we use for
the former.
Merge branch 'develop' of github.com:TheFuturistParty/debate into develop