Clean up admin on ready

https://www.pivotaltracker.com/story/show/62697818

This PR cleans up admin scripts, focusing particularly on admin on_ready.js.

Tasks:

- [x] Move all loose code out of on_ready.js.
- [x] Investigate which of the remaining initialisers are not global.
- [x] Move global initialisers into somewhere more appropriate and kill on_ready.js all together.