[#50] Save all dates as UTC in the database

At some point we may want to transform these to local time at the
dictization level. We will need a library like dateutil to handle it
properly though.
Merge branch '50-dates-in-utc'
[#50] Fix objects deletion on gather exceptions
Add a new command-line option 'job-sync' for running a job synchronously
with immediate output to the console.

This is much easier to use when debugging a new harvester, rather than
having to start gather and fetch queues on multiple consoles.