Bug 983712

I'm unclear who gets notifications of pull requests to mozilla/gcli. If you get an email about this and are not expecting it please comment on the pull request, and I'll work out what to do.

What this change actually does:
Using flex box means we can better control the layout of the menu. It was a table, but is now a flexbox containing 2 divs, one for the names and one for the descriptions.
Also we fixed some mouse selection problems.