Order destination groups by parent group, indent subgroups

NB: (Not quite ready for merge yet)

This sorts the destination groups by their parent group, indenting subgroups.

![image](https://cloud.githubusercontent.com/assets/750477/4180887/6e0ad1b4-3707-11e4-9589-cd71f56bc97f.png)

I pretty much hate this, but there are exactly 0 ways to style <option> elements; changing the text to include spaces is pretty much the best we can do, short of using a custom-rolled html select dropdown which uses divs.