BUG: Image resize allows skewing of image in IE (fixes CMS #791)

Including this plugin seemed like the most complete solution to this problem, and allows it to be removed when tinyMCE is upgraded (assuming they have fixed this issue). Uses a compressed version of the advimagescale fork from sourceforge (http://sourceforge.net/p/tinymce/plugins/186/), as it allowed for multiple tinymce instances.

Tested in Chrome, Firefox, IE8 and IE9.