Merge pull request #8 from Zeeraw/master

[hotfix] Unset job host if going from OnHold to Scheduled
Merge pull request #9 from Zeeraw/master

[hotfix] Have to update attributes manually.
Merge pull request #10 from Zeeraw/master

[hotfix] Clear transcoding_started_at and remote_job_id
Merge pull request #11 from Zeeraw/master

[hotfix] Instantly return job.
Merge pull request #12 from Zeeraw/master

[feature] Automatically invalidate transcoders if unaccessible for too long.
Cleaned up code