[WIP]Add backwards compatibility for pickled envs

[stevetorr]

• env.py should now be backwards compatible with old atomic environment objects without a cutoffs mask attribute
• Clean up PEP8 compliance for env.py and test_env.py

[codecov-commenter]

Codecov Report

Merging #189 into development will increase coverage by 0.01%.
The diff coverage is 96.00%.

@@               Coverage Diff               @@
##           development     #189      +/-   ##
===============================================
+ Coverage        60.90%   60.91%   +0.01%     
===============================================
  Files               44       44              
  Lines             8252     8257       +5     
===============================================
+ Hits              5026     5030       +4     
- Misses            3226     3227       +1     

Impacted Files	Coverage Δ
flare/env.py	98.43% <96.00%> (-0.75%)	⬇️

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