Stats Routes

[mxmeinhold]

I've started working on stats routes, beginning with a route to grab signatures over time for a single packet.

That route is /api/v1/stats/packet/<packet_id> and returns data in the format of

{
	'packet_id': '<packet_id>',
	'dates': [
		'<date>': {
			'upper': [ 'uid' ],
			'fresh': [ 'username' ],
			'misc': [ 'uid' ],
		},
	],
}

This should allow constructing a few nice graphs for #62, since the data is split categorically and temporally, but I think @devinmatte mentioned some other slices that would be useful, so I was hoping to get some feedback on both this formatting and what else might be helpful.