Youtube Videos and TLC for Summernote

Addresses issues #1670 ,  #1765 , and #1748 

This branch fixes some bugs introduced by my last patch, in addition to some long standing bugs related to Summernote.

**Change Summary:**

1.  Youtube Videos can now be added to Summernote by the new "Add Video" UI controls, copy and pasting a link, or using the "Add Link" button in the toolbar.
2.  The "Add Link" button now properly lets the user change the text to be displayed for the hyperlink.
3.  Added iframes to the list of tags to be sanitized.
4.  Moved all code related to processing iframes to the media object model
5.  UI fixes for Summernote (fixed maximum height, scaled the size of images and videos, Edit button now always visible to the user for ease of use and consistency with other Save/Cancel buttons, clicking on "edit" no longer spawns a second scroll bar, added word-wrap, etc).
6.  Added option for videos to be played in browser full screen mode.