Updated lexicon definitions addressing issue #56 #55

Sorry this took so long to get here. Life ended up getting in the way. On the bright side that let me get the new pulls v2 stuff covered too! The minor changes proposed here consist of subjective "correctness" changes like reordering field definitions and required fields as well more functionality related correctness changes like adding fields to the required section of some records and changing some things to be strong refed. Major changes are mostly related to decentralisation and all quite thoroughly documented in issue #56 in that group but special enough to be mentioned on its own: pull rounds as separate records! The central field of a round is the source field that defines the source of the requested changes. This is a union type of either a patchSource (pulls v1 style) or a commitSource (pulls v2 style). The repo source references the repo, a branch and a commit hash. The hash ensures immutable referencing of the changes. The repo location has been defined as a uri instead of an at-uri on purpose to be more flexible. This would eventually allow for tangled to have a feature almost no other git collaboration system (bar git itself) really has: Suggesting changes from a repo with arbitrary hosting! I don't expect this to be high on the list of priorities but I think it would be amazing if tangled let users suggest changes hosted on arbitrary hosts. Someone accidentally made a PR in a GitHub mirror with changes? No problem just get them to make a PR on tangled pulling in the GitHub hosted changes! In the process of migrating from another collaboration platform and still have some changesets hosted there that you want to bring on to tangled ASAP? Just make a pull!