Rename ticgit integration to tickets.

The current ticgit implementation is based on ticgit.net, a BSD
implementation for C#.  Jeff Welling advises using commit
bf57b032e030bd16a7b2 (2009-01-27) from ticgit as the last MIT licensed
commit.

A more complete implementation will be based on this version of the
original Ruby sources.  It remains unclear if I will support using the
"ticgit" branch name or not.  I purposefully haven't looked at any of
the GPL improvements by Jeff, but I can see from the readme at GitHub
that he has renamed the branch to "ticgit-ng" which I have no plans on
supporting as I do not want to taint GitBlit with GPL code.