Return promise from m.mount and m.route

[spacejack]

It would be useful to know when mounting & routing are complete in cases where your app needs to access the DOM (when not in a component lifecycle hook.) I've found with mount you need to wait 1 frame, with route you might need to wait 2 frames (including the redirect from / to /#! for example.)

Hopefully this will be easy when redraws are made async.

[tivac]

#1592 landed, so this may be worth investigating again.

[oliverhunt]

This would be a worthwhile feature for me