[skip validator]

Also adds another test for #9461: carousel next/prev should ignore non-items

Refs #14090.
Also, fix one typo.

faster and easier to test/develop js functionality not represented in unit tests, and gives us
a playground for interactions, etc.

It also makes it so developing javascript is now decoupled form jekyll, which should make everything
faster and less painful.

This commit also reverts my filter commit https://github.com/twbs/bootstrap/commit/9900771aa7f1b3ddcee49aec84082104776ace70
which broke scrollspy for dropdowns.

Be more consistent across the whole codebase.

Also, make use of JSHint's 2.5.1 `extends` and `qunit` options. This way we set our basis options in js/.jshintrc and override the rest.

* register the callback before invoking the toggling
* listen for `hidden` instead of `hide`
* account for the possibility of the associated `show` event being preventDefault-ed

Adds relevant unit tests.

Generates a unique id for tooltip and adds [aria-describedby] to the element
it is called on. Resolves issue #13480

- set up test
- linted the code styles
- passed the tests
- integrated feedback from @cvrebert

primarily adds a data- attribute to the tooltip (and thus, the popover)
to create a self-reference.