Added support for portable and hard-to-find KSP installs.

We now look in the local directory to see if we can find KSP
there. This means one can just copy the client into your
KSP install, and it will Just Work™.

Addresses part of #23.
Correctly detect Steam path from registry.
Moar exception handling in FileSystem.

Seriously.
Merge pull request #26 from Wizarth/steam-detect-winnt

Correctly detect Steam path from registry.