Add u-hidden visibility util and update comment style.
Use the html hidden attribute instead of a class.
Tweak the comments.
Visibility utils – Add tests.
Merge remote-tracking branch 'origin' into add-hidden-util
Merge pull request #57 from mobify/add-hidden-util

Add a hidden visibility util and update comment style.
Merge branch 'master' of github.com:mobify/stencil into fix-components-align