Proof Dependencies and Reasoner Conflicts

Until Rodin 2.1, proof status is determined from proof dependencies on the one hand and a proof skeleton on the other hand. The skeleton is entirely visited, searching for conflicts in reasoner versions. Hence the idea of integrating reasoners in proof dependencies and have them processed the same way as other proof dependency components, that are stored in the root element of the proofs to allow for quick access. This improves performances in updating proof statuses, which is by far the most time-consuming build operation.