Bugfix: Remove html5 video and source elements from full_html text format.

## Ready State: Yes

Removes html5 video and source elements.

## Requirements & Dependencies

* None

## Deployment Instructions

* Merge code.
* Rebuild module.
* Revert feature.
* Clear caches with `drush cache-clear all`

## Usage/Test Instructions

* Make sure htmlpurifier errors are gone.
* Test and configure iframe video embeds to work.