Implement SIP6

[braydonf]

Implements https://github.com/Storj/sips/blob/master/sip-0006.md

Part of: storj-archived/integration#5

[sk-pub]

Didn't find other place to comment the proposal.

Even if prioritization of farmers that are geographically closer to the user can improve current state it's not so good generally. Geographical nearness is not equal to network nearness. Host may be far away but have high-speed connection to Internet backbone. Prioritization based on shard transfer speed looks much better.

[aleitner]

Initial difficulty is too hard. None of my farmers can join the network

[braydonf]

Okay, added a method to initialize the settings.

[aleitner]

Init on redis start looks good

[braydonf]

Cool, added tests to make sure that those init values will be adjusted as expected, and added config options for farmer selection settings (no longer constants).