The autocomplete AJAX is identical to the version in tool_lp, but also
includes support for excluding suggestions (i.e. cohorts already
synced with the current learning plan).

As temporary editor files have been moved from core_h5p/editor to
user/draft, they can be removed (to clean unused DB entries).

If two different plugin types (e.g. theme, local) implement
override_webservice_execution callbacks, then all of them except
the 'last' plugin type do not work correctly.

- for this issue the atto styles.css was moved into theme boost so
we can use our preset variable for $gray-500