Allow Orgs to hold tokens of other Orgs

[iamdefinitelyahuman]

It should be possible to set up a ZAP org that invests in other ZAP orgs - a sort of investment fund:

• ownership can be handled via a type of Custodian contract
• identify checks against individual org KYC registries can be performed whenever fund ownership changes
• members in the fund can use the (as yet undeveloped, Expand governance functionality #14) governance functionality to determine how it is run, what it invests in, when and how profits are distributed, etc

There are significant legal considerations in such a setup - @lex-node you will have to provide a lot of sanity checks in the review process on this one :)