Sections as Many2Many

I redid the logic linking Sections to Auth_Users because I could not figure out what is getting screwup up with the database migrations (web2py's DAL leaves quite a bit to be desired)

I removed the section field from Auth_User and moved section code into its own file.

Users are linked to sections by a secondary table. All logic for getting, setting and deleting models is included into the Sections model. The views simply include logic for controlling input.