Storagemarket/provider allows subscription to events

[shannonwells]

WAT

closes #77

HAO

• Allow consumers to subscribe to StorageProvider events.
• Use @hannahhoward new generic threadsafe pubsub for subscription management

Questions

I'm sending the entire deal to the subscriber. Not sure if that's what we really want though.

[shannonwells]

I kept paging too far down looking at stuff, so I figured a comment might help

[codecov-io]

Codecov Report

Merging #202 into master will decrease coverage by 0.74%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #202      +/-   ##
==========================================
- Coverage   67.88%   67.15%   -0.73%     
==========================================
  Files          40       40              
  Lines        2117     2161      +44     
==========================================
+ Hits         1437     1451      +14     
- Misses        573      601      +28     
- Partials      107      109       +2     

Impacted Files	Coverage Δ
storagemarket/impl/client.go	0.00% <ø> (ø)
storagemarket/impl/provider.go	6.20% <0.00%> (-0.79%)	⬇️
storagemarket/types.go	33.34% <ø> (ø)
retrievalmarket/network/deal_stream.go	65.39% <0.00%> (+15.39%)	⬆️

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[hannahhoward]

Please remove go routine and fix test
Convert providerSubscriber to take a MinerDeal value, not a reference. Passing the whole deal is correct but should not be a pointer.

[hannahhoward]

LGTM and that's a really good test for state flow.

[hannahhoward]

Love this check!