Use Ace editor?

I've added the [Ace editor](http://ace.c9.io/#nav=about) to my installation of Gitit to use with Vim mode. Would you be interested in a pull request that added Ace? I've implemented it as a hack with my own idiosyncratic preferences, but I can add it with sane defaults if you wanted to ship it with gitit.


The issue names no files, tests, or entry points. Start by reviewing Gitit's current editor integration and the linked Ace editor documentation, then clarify the desired Vim-mode behavior and sane defaults. Done would be a pull request adding Ace with agreed defaults and working Vim-mode editing.

Written by the indexing model from the issue text.