userportal: allow links in MOTD

- Added the ability for admins to add links in the
  MOTD in the user portal. These links are checked
  for safety before being added into the MOTD.

Change-Id: I6c78c9e6d6dc9417e22c71dab66ae4507ea5c191
Signed-off-by: Alexander Wels <awels@redhat.com>