The patch introduces a new field 'timecopied' that holds the timestamp
of when the given form was cloned last time. Using this field, we can
decide whether the form can be actually re-shared or not.
Note that the logic just hides the icon. It is meant as a usability
feature, not any real protection from sharing.
There is a new capability to manage all shared templates. Without this
capability, the user is allowed to delete just templates they previously
shared.
In the future, an option to edit the template directly might be added.
At the moment, the workaround is to pick the template into a temporary
assignment, edit it there and re-save it as a new template.
Every grading form can be basically in either DRAFT state (currently
being edited) or READY state (available for usage). For shared
templates, the status is not relevant at the moment and they are
automatically in the READY state.
The patch introduces a new script templates.php that allows to search
for a previously shared form (template) and re-use it.
The patch also modifies the preview rendering of grading forms. Now
plugins are responsible for rendering the form itselft, without any
headers, descriptions etc (we need to embed the form preview into
various places so the caller looks after the frame).
