Remove redundant 'shortcuts' directory in linuxclientsetup
Remove unused .xcf file in linuxclientsetup/images
Use '-' to separate words in paths for consistency

All scripts, utilities, directories and images (with one exception) now use
'-' as a word separator, rather than the previous differing standards of '-',
'_' and no separator at all. This should increase consistency across naming.
Although admin_skel has been renamed to admin-skel, there is compatibility code
for legacy server files using admin_skel instead.

The exception to this rule is linuxclientsetup/images/smalllogo.xpm. This is
because it appears XPM files encode their filename as a variable inside, so
changing the filename may break the image. Still, it doesn't use an underscore,
so I guess it is OK.