Enhance Protean Flask to be compatible with Protean 0.0.11

[subhashb]

• Remove Pylint and retain Flake8 as the linter mechanism
• Clean up test cases and use pytest fixtures
• Upgrade package versions where possible

[codecov-io]

Codecov Report

Merging #18 into master will decrease coverage by 0.02%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #18      +/-   ##
==========================================
- Coverage   90.76%   90.73%   -0.03%     
==========================================
  Files           9        9              
  Lines         314      313       -1     
  Branches       38       38              
==========================================
- Hits          285      284       -1     
  Misses         14       14              
  Partials       15       15

Impacted Files	Coverage Δ
src/protean_flask/core/serializers.py	86.84% <ø> (ø)	:arrow_up:
src/protean_flask/core/base.py	86.56% <ø> (-0.39%)	:arrow_down:
src/protean_flask/core/views.py	89.58% <100%> (+0.07%)	:arrow_up:

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