Fixes for Sheriffs' Treeherder backfilling and scheduling support

Sheriffs have the ability to backfill jobs on Treeherder (to determine the push where are regression starts) and the ability to run missing jobs on a push (due to coalescing/SETA).

Few weeks ago we added alerts to pulse_actions:

• System exit calls where crashing pulse_actions and we did not notice

 and we've fixed a couple of bugs since then:

• Backfilling of a test job of pushes with coalesced builds should not test against the wrong build
• Thanks @KWierso for reporting it!
• Filling in a revision on aurora partially fails

Other changes:

• Better documentation
• Moved under the Mozilla Org on GitHub
• Added auto deploy to Heroku from the 'heroku' branch

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This work by Zambrano Gasparnian, Armen is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.