Incorporate the TinyMCE tests into our JS tests:
- Modified the original tests so TinyMCE can be loaded from /src/wp-includes/js/tinymce.
- Added "WP" option to the UI to select only tests relevant to our integration (excludes most of the default plugins tests).
- Added tests for obsolete HTML elements and attributes (html4 back-compat).
See #27014.

git-svn-id: https://develop.svn.wordpress.org/trunk@27155 602fd350-edb4-49c9-b593-d223f7449a82