Add xmobar 0.21 with all_extensions

Packages and logs at https://spideroak.com/browse/share/kmicu/archpkgs/archpkgs/xmobar/

I'm still not sure how to generate multiple xmobar packages - e.g. xmobar with default flags (minimal) and xmobar with all flags like this package.

I adjusted flags in xmobar.cabal patch before adding package with cblrepo and added non-hackage dependencies in xmobar.pkgbuild patch - I'm not sure if this is an idiomatic way though.