Polish the Human Icon Set for Ubuntu

Polish and extend the current Human icon set with icons that are missing in critical places.

UNIFY: ubuntu fonts for Ubuntu

Unify font sizes and types for certain aspects of the op- erating system. An extensive preliminery review of this spec is here: https://wiki.ubuntu.com/ArtworkTeam/Drafts?action=AttachFile&do=get&target=Ubuntu-6.06-Improvement-Review.pdf