Updated video plugin
The frontend does not have to specify a height or width for a template anymore.
Enable CORS access to the frontend JSON endpoints.

This is disabled for all non-public instances.
Keep the template URLs relative, my bad.
Keep throwing an error when the template width and height are invalid.

Also add a test to ensure that not setting them is OK too.
Merge branch 'master' of git://github.com/concerto/concerto into rails-4

* 'master' of git://github.com/concerto/concerto:
  Keep throwing an error when the template width and height are invalid.
  Keep the template URLs relative, my bad.
  Enable CORS access to the frontend JSON endpoints.
  The frontend does not have to specify a height or width for a template anymore.
  Updated video plugin

Conflicts:
	Gemfile.lock