Switch SVGEdit to use the master copy from Google Code instead of a local copy.

Local copy no longer exists since we switched from SVN externals to git.
Master copy is also more up to date and works on IE 9.

Note that SVG-Edit is embedded via an iframe, so the only security leak
should be referrer information and the actual contents of the file.

A custom copy of SVG-Edit can still be embedded by switching $wgSVGEditEditor.

Change-Id: Ic55951482ed9e0d4a7cd5de17011614ec2a446e5