Circles 2.0 Removing trust limits and splitting the hub contract

[louilinn]

Contracts update discussion https://aboutcircles.com/t/earth-circle-ip-1-circles-2-0-architecture/428/16

This issue in particular: https://aboutcircles.com/t/earth-circle-ip-3-web-of-trust-module/447

Trust limits:

The new HUB2.0 contract will have new implementations of transferThrough() and checkSendLimit(), which should ignore trust limits (and only interpret binary trust).

Separate the Hub into 2 contracts:
- The bits are in favour of separating Trust functionality in a different contract (called TRUST), although we don’t see it as necessary.
- The TRUST contract should in that case be very simple.
- We think that it might not be necessary to create a new TRUST2.0 contract since there is the old HUB that already stores all the trust relationships and trust() method.
- If trust rules (besides trust limits) are not going to change, we think a new contract is not needed. In the transfer contract, we can interpret any trust limit different than 0 as 100%.
- Or if we have a new TRUST contract, there are 2 options:
- Migrate trusts from the old HUB (HUB1.0) to the new TRUST or HUB2.0 contract
- Keeping trust in HUB1.0
in HUB2.0 there would be new implementation signup() method, and new userToToken and tokenToUser mappings
in TRUST contract we would just call trust() and checkTrust() in HUB1.0 with the trust limit = 100
- We have to discuss further if we prefer migrating trusts, or just read /write in HUB1.0. But we are inclined to not add extra unnecessary steps that may lead to errors or bugs in the migration of the Web of Trust.