Three known methods:

~/.wm_style - WDM
~/.dmrc - KDM
/etc/X11/xinitrc and ~/.xinitrc - startx

Must therefore keep track of:

xinitrc.NAME
Session=NAME
cat ~/.wm_style -> NAME

Ugly (but necessary) - build reverse lookup from menu choice: translated -> key

If running as root, allow global setting - set xinitrc

Setting the window manager should be factored out to something like
VASM::Utility::FileSystem::WindowManager
