Add require method

[bkaptijn]

With require() one can denote an abundance service requires the actor in need to have a claim with a certain predicate and requires this claim to be attested by a given other SSID as attestor that used a given second predicate.

require (serviceSsid, predicate, attestorDid, attestPredicate)

The service can use the core verify() method to assert the requirement before offering a solution. A service can match a need before all requirements are met as some requirements may involve information that needs to be communicated over more private channels