Jenkins job number

Adds a jenkins job number to StatusCheckResult model; this allows cabot to link directly to the failed job in a hipchat message and prevents generating multiple StatusCheckResult instances for the same build which makes the debounce mechanism less reliable.

I ended up attaching the field  to the StatusCheckResult model partly as there is no JenkinsStatusCheckResult model but mostly the desire to be consistent with currently model ORM layout of keeping the fields on the parent model.

The StatusCheckResult duplication should stop situations where cabot checks the same job multiple times and reports each one as fail (and then alerts). We've learnt nothing new by creating a new check and I'd argue it's better to have more control with the debounce option to manage when cabot will alert.