Earth Circle IP 4 - Default Transitive Transfer Module

Based on the recent discussions from Earth Circle IP 1 - Circles 2.0 Architecture, I am pulling out the essence we agreed on so far.

The new transitive payment modules should be an opt-in extensions, where each user can give allowances to one or many transitive payment modules.

The first default payment module removes the restrictions of the original transferThrough method and builds on top of the binary web-of-trust contract.