Support cursors in ace

This is the minmal amount of work I had to do to get different
color cursors appearing in ace. It involved:

- creating functions to convert ace ranges to cursors and vice versa
- reaching into the ace internals to render cursors
- emitting cursor events from the server to opened docs
- add a couple cursor tests
upgrade to newest version of ace
switch to text2 OT type
Merge pull request #180 from mad-eye/ace-cursors-support

Support cursors in ace