Implement PUT on /corpora/{corpusname}/play/{playname}

[cmil]

As a second step after #44 I suggest to implement PUT and POST on a single play. This would accept a TEI document and would create a new or update an existing resource in the database. This would allow us to add or update a single play without depending on a Github push or reloading the entire corpus.

[cmil]

PR #50 doesn't implement POST since PUT on either new or existing URIs is sufficient for creating and updating documents.