When deploying a site extension deploy its WebJobs.

The site extension needs to have the WebJobs under `App_Data\jobs\{job type}\{job name}`.
The jobs will be moved (not copied).
The result WebJob name will be `{site extension id}({job name})`.
Fixes #1393
If `CleanupExternalJobs` failed above, some of the folders will be left, and this will almost certain fail. Probably need more error handling here.