[mkcal] Nuke unused tracker support from orbit.

No idea why this wasn't done earlier, but the net impact is a ~50kb decrease in
post-stripped binary size.
[mkcal] Remove apparently unused DirectoryStorage class.
[mkcal] Remove QtLockedFile solution.

This was all a gigantic lie. It was never really used, but dated back to the start of
the repository. The only "use" of it was in the #include in DirectoryStorage,
which was removed in 6d6ae174fe491aa19462cced8159224dec697313.
Merge pull request #14 from rburchell/master

[mkcal] Nuke unused stuff from orbit.