Workaround for plus signs in email addresses

Gmail email addresses containing plus signs cause problems with
taxonomy terms and taxonomy searching. This fix stores + as .PLUSSIGN.
in the database as a workaround.
Updated iconography

Moved most of the functional icons to a sprite.
Minor adjustments to group list css

Fixes problems with display of really long group names and adds a
one-column version of the list for smaller screens.
Merge pull request #98 from dcavins/group-list-css

Group list css changes