Ad-hoc filter for UbiCast Atto plugin
This filter alleviates the problem which arises when atto_ubicast tries to inject an HTML tag directly into Atto. This works for teachers and "trusted users" but not all users.
Starting in the next release of atto_ubicast, an HTML tag will be injected instead. This tag's usage is unrestricted and is then turned into an iframe at the rendering stage by this plugin.