Create admin setting for group name

[tobiasreischmann]

• Add an admin setting 'group_name' from type text. Use a heading section "Access Policies".
• Change apibridge->create_acl_group() so that the group name from this setting is used as $params['name']. Since the static function api::get_course_acl_group_name from the repository plugin is only called here, this functionality can be moved to the block!
• Allow placefolders [COURSEID] and [COURSENAME], which are automatically replaced by course->id and course->fullname. You can use str_replace() for that. (http://php.net/manual/de/function.str-replace.php)

[tobiasreischmann]

Currently the code distinguishes between get_course_acl_group_name, which is "Moodle_course_" . $courseid, and get_course_acl_group_identifier, which is "moodle_course_" . $courseid.
@ebbertd: Do you have an idea, why and how opencast distinguishes between these two values?

[tobiasreischmann]

We identified the responsible code in Opencast:
final String groupId = name.toLowerCase().replaceAll("\W", "_");
So we need to reproduce this call in our code. The admin setting determines then the group name only and we calculate the identifier from it.

[tobiasreischmann]

Additionally there seems to be a restriction of group name length to 128 Byte. I would suggest to add a hint to the admin setting, that all characters exceeding this length, will be cut. The admin has to make sure that distinguishing characters, like courseid, will not be target of these cuts!

[tobiasreischmann]

We definitely need to test special characters as ä, ö, ü and ß here, because they might occur in course names. The above code is Java. In Java \W matches everything, which is not in [a-zA-Z_0-9].