Add multi-org token resolution features to CiviMail

In CiviMail for

{org.*}

tokens in a multi-org environment, we need a way to resolve which org's data to pull in for each recipient contact. That should work as follows:

1. All mailings must be sent to one or more groups (even if they are going to a search result subset of those groups, the recipients can still be traced back to those groups).
2. For each contact, arbitrarily choose one of the groups they're a member of AND the mailing is being sent to and traverse up the hierarchy to the parent org to get the org token values.
3. Cache these values so when they show up for other contacts in the same group, they can be inserted quickly from the cache.