HTTP API should return new job version on POST /v1/jobs

When posting a job using the HTTP API, nomad should return as part of the response, along with the created evaluation id, the now job version.

My use case for this is to have the job version so I can then query `/v1/job/job-name/allocations` and detect failures related to this new job version (and filter out allocations from previous job versions). For batch jobs, this is the only way I see to detect failures as the job overall is marked `dead` regardless of the status of the last allocation.

A useful addition to the API would be to include the job version for the `/v1/evaluation/eval-id` endpoint, for the same reasons.