As a course admin, I want to allow roles in the UI for ACLs that match a pattern

A common use-case in integration scenarios is to add roles to Series ACLs to permit members of a course to access recordings in a series.

This may be the case where users authenticate via LTI or a user directory provider, and the roles may be of the form courseid_Learner or courseid_Instructor. courseid is typically numeric.

Discussion thread here:

https://groups.google.com/a/opencast.org/forum/#!topic/users/MoXORV9hoAY

It is proposed to add this ability to the CustomRoleProvider so that a regexp pattern may be specified in /etc/custom.properties, e.g.

org.opencastproject.security.custom.roles.pattern=0-9+_Learner

The ACL editor in the Admin UI will then call findRoles() to validate a role name that is manually entered (typed in rather than selected from drop-down list). If the CustomRoleProvider matches the regexp it will return the offered role name from findRoles and so the role will be permitted.