Also fixed /dev/null reference due to deletion change.

This is for history where we specify two revs to diff, not just a
commit against its parent.

The current ticgit implementation is based on ticgit.net, a BSD
implementation for C#.  Jeff Welling advises using commit
bf57b032e0 (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.

Settings access has been abstracted and the way is becoming clear to
offer a WAR build in addition to the integrated server stack.  Util
methods moved around.

Right now the implementation is hard-coded to pass the realm into a
singleton.  This won't work for a WAR distribution so I will
need to figure out how to properly authenticate the webapp using form
authentication and the git servlet using basic authentication - host
against the same realm.

This seems to improve page loading times.

Added placeholder for Admin links on main page.
Dynamically add ticgit link to nav links, if ticgit branch is
discovered.
Settings refinements.