Fixed reveal closing randomly all .flex-videos from document

In the context of the function, this refers to document, so when you do $(document).find('.flex-video') and then set the iframe src to about:blank, all videos on the website are dying.

The huge problem is that this method is also called by alert-boxes, dropdowns and so on.
updated docs html
Merge branch 'master' of github.com:zurb/foundation
remove slide_selector from docs, not available until 5.1.0
Merge pull request #4226 from OtaK/master

Fixes #4036 Fixed reveal closing randomly all .flex-videos from document
Fix duplicated ids

The id `right-label` is duplicate, and colides with doc/includes/form/examples_form_inline_labels.html. To replicate the issue just click in the `label.right.inline` in http://foundation.zurb.com/docs/components/forms.html
Merge pull request #4256 from kuroisuna/patch-1

Fix duplicated ids in label.inline.right example
Merge branch 'master' into seantimm/topbar_test_cleanup