This very simple block is a clone of the HTML block that allows some third party to change content
if allowed by a capability.

This block is usefull for course 'templating' when primary authors need to setup place holders for
late editing.

Users allowed will be able to change content even if they have no access to course editing mode.

Full course authors may "lock" the content at any time by configuration (thus needing editing mode), so editable
HTML block behaves as an usual HMTL block.