1.6 link choosers

This is a reroll of #179 originally started by @liamkeily.  This PR retains the functionality intended by the original PR with:

- remove unrelated changes (moving tab into boxes)
- remove some unneeded javascript file
- changed the population of `Menu.linkChoosers` from within a component to use events
- dialog content is loaded via AJAX (instead of inlined)
- lots of CS fixes

I would appreciate help in testing and any comments for improving this PR.