[Super] Group refactor

[kindly]

This is the implementation of the final draft in

​http://wiki.ckan.org/Groups_Refactor

Steps to complete this will follow (somewhat) in the following order.

Change package_group table to membership.

• model migration.
• simplify revisioning
• Remove any sqlalchemy releations from groups.
• change logic functions

Single type per group

• migration add type to group table.

Add capacity table

• model migration.
• add to logic functions.

Allow other objects to be added to groups.

• change logic functions

Adapt thedatahub.org to use new model.

• move auth groups over to groups/members
• change user_object roles to use groups? keep user object roles for time being.
• make create update package/group put the correct items in the group/members/capacity tables.
• work out how ui works.

Create model for dgu.

• adapt auth functions to use auth.
• adapt package_create/update group_create/update to fill in the correct capacties/members.

Adapt Iati, and potentially other custom instances.