update emailer with priority and timestamp
update emailer with priority and timestamp

- uses new columns priority and timestamp
- definitions were updated in the undefx/Automation repo
- table automation.email_queue was manually updated on midas
- add command line arg `limit`, which defaults to 100, and determines 
the max number of emails to send at once

cmu-delphi/operations,cmu-delphi/operations,cmu-delphi/operations