TinyMCE Plugin: Added media plugin to TinyMCE for the Annotation tool

**Background:** We noticed after our transition to using edX's version of TinyMCE that we were missing some key plugins that we had touted in previous courses and that should be implemented. I followed the rules under the BUILDME.txt file in the tinymce folder and included the "media" plugin. This also includes a quick change to the css for a missing class name in share-annotator.css

**Studio Update:** TinyMCE should now be able to have a media button.

**LMS Update:** Same as studio, the annotation tool TinyMCE instance should now have a media button. Also, the fix to the css file will fix a padding/margin issue in the editor view for the "Share this annotation" button. 

**Testing:** Using the following [tarball] (https://www.dropbox.com/s/r684ber7z4ddqtc/2014_T4.DPRfFs.tar.gz), you can create a test course. Go into any of the annotation tool units and highlight to create an annotation. Open up the editor. There should now be a media button. Press it and paste a link to a youtube video. Save the annotation and you should now be able to see the video in the pop-up and in the table below. The other fix prevents the Share this annotation and button from being misaligned in the editor.