Merge pull request #1849 from twobraids/hang-comment

No Bug -- added comment about meaning of the processed_crash.hang_type
fixed integration test invocation
refactored crontabber to use transaction_executors
added some docs about the PG cronjob base classes
added transaction decorator to all methods database methods
more changes based on review
ensure rabbitmq is empty before doing any tests that touch it
added mixin decorators & convenience classes
reworked bugzilla crontab job to better organize transactions