Huobi: Add Subscription configuration

[gbjk]

Just adds configurable subs.

This PR does not fix auth WS usage, which appears broken due to using deprecated v1 paths.
Also doesn't seek to make subs synchronous.

Stacked Dependencies

• Kucoin: Add subscription templating and various fixes #1579

Type of change

• New feature (non-breaking change which adds functionality)

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 22 lines in your changes missing coverage. Please review.

Project coverage is 36.52%. Comparing base (b602d54) to head (554f69c).
Report is 29 commits behind head on master.

Files with missing lines	Patch %	Lines
exchanges/huobi/huobi_websocket.go	37.14%	22 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1604      +/-   ##
==========================================
- Coverage   38.22%   36.52%   -1.70%     
==========================================
  Files         422      414       -8     
  Lines      152222   179325   +27103     
==========================================
+ Hits        58184    65503    +7319     
- Misses      85984   105951   +19967     
+ Partials     8054     7871     -183     

Files with missing lines	Coverage Δ
exchanges/huobi/huobi_wrapper.go	39.89% <100.00%> (-2.59%)	⬇️
exchanges/subscription/list.go	100.00% <100.00%> (ø)
exchanges/subscription/subscription.go	100.00% <ø> (ø)
exchanges/huobi/huobi_websocket.go	29.87% <37.14%> (+1.24%)	⬆️

... and 396 files with indirect coverage changes

[shazbert]

Good stuff, minor potential nit

[shazbert]

LGTM.