Refactor/split utils into submodules

[randomir]

Related to #437.

Enables import time optimization.

[codecov]

Codecov Report

Attention: Patch coverage is 91.22137% with 46 lines in your changes missing coverage. Please review.

Project coverage is 88.41%. Comparing base (7bc2a1d) to head (f577411).
Report is 158 commits behind head on master.

Files with missing lines	Patch %	Lines
dwave/cloud/solver.py	31.57%	13 Missing ⚠️
dwave/cloud/utils/cli.py	78.04%	9 Missing ⚠️
dwave/cloud/utils/logging.py	90.32%	9 Missing ⚠️
dwave/cloud/utils/dist.py	63.63%	8 Missing ⚠️
dwave/cloud/cli.py	77.77%	2 Missing ⚠️
dwave/cloud/utils/decorators.py	98.78%	2 Missing ⚠️
dwave/cloud/utils/coders.py	96.55%	1 Missing ⚠️
dwave/cloud/utils/http.py	98.03%	1 Missing ⚠️
dwave/cloud/utils/qubo.py	97.43%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #628      +/-   ##
==========================================
+ Coverage   88.22%   88.41%   +0.18%     
==========================================
  Files          33       42       +9     
  Lines        4527     4558      +31     
==========================================
+ Hits         3994     4030      +36     
+ Misses        533      528       -5     

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[arcondello]

I didn't look too closely at the functions because I believe most of them have just been moved. Structure seems like a nice improvement.