Added support for minimal zim desktop wiki package.

Work pretty well on my branch based on nixos 14.04 commit: 3e4e106:
https://github.com/jraygauthier/nixpkgs/tree/jraygauthier

Not sure however if I should propose this pull request for the 14.04 branch as well?

Tried to install as well using the master branch. It built and installed well but failed to run.