in-progress work on modals
updating to follow latest liquid-fire release
keep cacheSize with goAbsolute

This is a followup to f2e2f55ea230fa7b776c8faa6673b86d1c41a639
Merge branch 'master' into modal
visibility control for modal popup transition
vertical centering modals: stick with happy standard flexbox for now
adding a scenario
bugfix: pass growth-control options through liquid-with
Merge branch 'master' into modal

Conflicts:
	app/router.js
make modal animation run even at initial insertion
modal controller mixin
working modal controller mixin
lots of progress on modals
modal dismiss protocol
tab trapping
more tab focus control
adding accessibility attrs
don't append modal container until needed
documented modals
minor style precedence