Fix hover-tooltip flickering when mouse re-enters

- is(':visible') seems to be the only reliable check, without a refactoring of how hoverState is used
- tests need improvement
Add section to docs explaining our stance on validators
Address #14541 by tweaking badge docs

* move unrelated .btn-primary example out of the pills subsection
* remove excessive .nav-stacked example
Merge pull request #14543 from twbs/validation-docs

Add section to docs explaining our stance on validators
Merge pull request #14546 from twbs/address-14541

Address #14541 by tweaking badge docs
Fixes #14545: Avoid strange formatting on vendor prefixing for placeholder
Merge pull request #14273 from sgonyea/master

Fix hover-popover/tooltip flickering when mouse re-enters
Update dependencies.
Run `grunt`.
Fix bug not re-calculating scrollbar width when opening modal.

If opening a modal when a scrollbar is present, closing it, then
resizing the window so the scrollbar disappears, then opening the
modal again, the content would shift. This fixes the problem by
always calculating the scrollbar width every time a modal is opened.

Closes #14357.
Merge branch 'stefansundin/master'
grunt
Collapse accessability

Added tab-role, aria-selected, and aria-controls into the collapse html
docs.

Added support for toggling aria-expanded, aria-selected, and
aria-hidden via the javascript collapse events.

References issue #13555.

Sweet example at
http://accessibility.athena-ict.com/aria/examples/tabpanel2.shtml