Allow connecting Organization contacts to Groups for multi-org support

If a user has the (new) "Administer multiple organizations" permission, they should be able to connect Organization contacts to Groups (one-to-one relationship) to represent a multi-org hierarchy. The org contact holds info about the org itself (name, location, etc.) and the group holds other sub-groups/contacts related to that group (employees, alumni, online activists, members, etc.).

When linked, the org contact page should link to the group and any display of the group should link to the org.

Among other things, this link will be used by CiviMail tokens when sending a mailing to a group to determine org-related token values (for example:

{org.name}

,

{org.logo}

, etc.).