use datetime.datetime.utcnow() to create timestamps

closes #27

ENH: Refactor module

Expanded upon the Group's regex patterns.

Both _id and name now require a letter or number at the start and end, and enforce the minimum and maximum length.

Fix arbitrary path access

Optional NewRelic support

Zipfiles, mark 2

Proper group and user schema

Fresh installs should work out of the box.
Migration instructions for existing installs:
db.users.update_many({}, {'$set': {'created': datetime.datetime.utcfromtimestamp(0), 'modified': datetime.datetime.utcnow()}})
db.groups.update_many({}, {'$set': {'created': datetime.datetime.utcfromtimestamp(0), 'modified': datetime.datetime.utcnow()}})

Tune up jobs API