Wait for the expected target during a collapse

Document @icon-font-path & @icon-font-name more

Actually wait for the collapsed item to complete. If complete is called
with other target, instead of simply returning and do nothing, wait again
until the proper target triggers the event (otherwise this leaves collapse
in a broken state).

Remove unused javascript

Closes #11281 by merging it (after rebasing & resolving conflicts)

Add flexbox-based equal-height grid columns as an experimental example

Fix carousel-control margin asymmetry

Fixed typo in Responsive Tables CSS docs

X-Refs:
https://github.com/twbs/bootstrap/commit/b2a67ffe55f5fedb0ae1d5dff331687c3e744be0
https://github.com/twbs/bootstrap/commit/c97e6d5cad74d20257d28734f85311ef5d00b560

Replace $.fn.bind with $.fn.on in alert docs

document that label.active on preselected inputs in btn-groups is manual

move some caching info+logic out of .travis.yml

doc how to change the collapsed mobile navbar breakpoint