Stringify ticket links as "#123: Subject"

Removes the leading "Ticket" from the description to save space and
avoid repetition.  Unqualified numeric IDs are presented as and assumed
to be ticket IDs in many places and user input throughout RT's various
interfaces.  Links to other object types are still qualified, such as
"Article #123: Name".
Merge branch '4.2/concise-ticket-link-descriptions'