Add workflow version to classifications

Closes #254
What about the case when a user submits a classification for workflow version 1 and the project owner updates the workflow between subject load and classification receipt. The classification may be inconsistent with the workflow version that created it and possibly incorrect for use in consensus. I realise that this should not occur very often so perhaps it's a null issue that may only affect a small % of the classifications.

One solution would be to push the workflow version into the client and require this on classification submission to ensure consistent versioning.