Use latest revision's title in all review actions

This hotfixes #95 and should replace all improper uses of the proposal's title with the latest proposal version's title.

A cleaner approach would be supplying a non-null template variable which points to the latest proposal, whether there were revisions or not, and just referring to that proposal's title.  This would also clean up the whole ``{% if proposal_version %}{{ proposal_version.yadda }}{% else %}{{ proposal.yadda }}{% endif %}`` business all over the templates.

These commits go untested.