Allow jobs to be filtered by tool_id and history_id as well as by state. The tool_id is compared with the like operator.
Reduce a little code dup in api/jobs.py.
Modify jobs index to allow exact or inexact tool id filtering.

Discussed this with JJ and Dannon. Formerly this was only inexact matchings, I was a little worried about API users expected exact tool id matches when using a parameter called tool_id. JJ's original intended behavior can be accessed using tool_id_like.
Merge JJ's pull request #315 (with minor modifications discussed with JJ).