refactored crontabber to use transaction_executors
rewrote mixins.py - refactored all crontab apps

Conflicts:
	socorro/cron/jobs/bugzilla.py
pep 8 & pyflakes cleanup
Merge pull request #1745 from twobraids/crontabber-transaction

fixes Bug 950735 (v78) -  refactor crontabber to use the transaction_executor