KNL-1181 Cleanup LinkMigrationHelper.

This adds some JavaDoc and tests to LinkMigrationHelper. It also removes the static cover to make testing easier with the injected serverconfigurationservice.

git-svn-id: https://source.sakaiproject.org/svn/kernel/trunk@306141 66ffb92e-73f9-0310-93c1-f5514f145a0a
KNL-1182 Make PermissionException extend SakaiException.

This should probably have been in the original commit that introduced SakaiException but got missed.

git-svn-id: https://source.sakaiproject.org/svn/kernel/trunk@306142 66ffb92e-73f9-0310-93c1-f5514f145a0a