claim model

@elf-pavlik @bhaugen This is to replace the removed Reciprocity, which created Commitments from Economic Events. It was observed that Claims are different than Commitments because commitments can only be committed by the provider, while claims are initiated by the hopeful receiver.

Model looks like this. Claim has most of the properties of I-C-E- flows. Claim basically references both the event(s) that triggered the claim and the event(s) that resolve the claim. [edit: WRONG model, see following comments]

I included a brief description in the flows page. Probably a lot more could be said eventually.

The terms are straight out of McCarthy / REA.

Note REA people also talk about claims and 'negative claims'. Negative claims are things like issuing dividends. I haven't defined those here, not sure if we want to do that, or consider those commitments. My impression is the 'negative' term comes from enterprise perspective, not independent perspective. And if an agent doesn't get their dividend as expected, they could issue a regular claim.