Dynamically set/remove `aria-modal="true"` when a modal is shown/hidden

This reverts commit 11da1601.

This is no longer needed with jekyll-toc 0.9.1.

We have /site/.eslintrc.json that covers this.

This reverts commit b442ce31.

Callouts are already excluded from ToC, but due to a limitation in jekyll-toc they are still being included.

We should revisit this if the bug is fixed later.

It's pretty small compressed; a little less than 1 KB with gzip.

Image by @mdo.

This should reduce the amount of bytes for non-2x displays.

It's been macOS for 3 years now and we use just 'macOS' elsewhere in the Bootstrap documentation.
https://en.wikipedia.org/wiki/MacOS

* prevent text selection for floating labels
  * expand the click target by no selecting the label text
* use `pointer-events: none;` instead of `user-select`
  * thx @MartijnCuppens

This reverts commit b04f97f6.

The latest (2.6.2) docsearch.js version now displays results as standard `<a href>` links, allowing users to `ctrl`-click on them to trigger default browser behavior of opening in a new tab.

To maintain backward compatibility, this behavior has only been enabled to users that didn't define their own `handleSelected` method.

This PR updates your `docsearch()` code to take advantage of the new `<a href>` template, by removing your custom `handleSelected` and moving its behavior to the `transformData` call. Namely, what you wanted to avoid was jumping to the first `<h1>` of the pages, which would prevent users from seeing the header. This PR checks if the suggestion targets the `#content` anchor (meaning it goes to this first `<h1>`) and remove it.

Behavior should be the same, but at least now you can enjoy the `ctrl`-click :)

Previously we were using the old holder.js colors.