.xinitrc: don't hard-code xmonad path

xmonad may be installed via cabal and live in ~/.cabal/bin.
.xmonad; don't print layout in xmobar

Layouts are usually long complex names.
.xmobarrc: make compatible with xmobar-0.15

0.16 is buggy, and 0.15 doesn't accept some options we don't care
about.  So remove those options.