Steps towards removing globals and allowing multiple svg components to exist.

Make a new SvgComponent that inherits from goog.ui.Component and use it within inject to create/populate the containing Element.

BUG=104

Review URL: https://codereview.appspot.com/7235043

git-svn-id: http://blockly.googlecode.com/svn/trunk@599 c400ca83-b69d-9dd7-9705-49c6b8615e23