WIP - Sticky scrolling container

[phazei]

This actually does stick properly inside scrolling divs. All that remains is getting the positioning right for positioning the elements with css transform: translateY since position fixed doesn't work in scrolling divs

[phazei]

Put this here if someone else wants to complete it, not sure I'll get to it and it's pretty close...

[harm-less]

Hey @phazei,

Thanks for the effort of trying to make work. It's a lot of code changes and I'm not sure what's happening with Travis CI, but the build isn't passing.

You or someone else can definitely finish it up :)