Support backward compatibility for Quince earlier releases

[farhan]

• ticket: Remove xblockutils and migrate to xblock.utils #176
• Support backward compatibility for Quince earlier releases
• Update release version

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (329b6e9) 56.36% compared to head (c474cb4) 55.17%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #186      +/-   ##
==========================================
- Coverage   56.36%   55.17%   -1.20%     
==========================================
  Files           3        3              
  Lines          55       58       +3     
==========================================
+ Hits           31       32       +1     
- Misses         24       26       +2     

Flag	Coverage Δ
unittests	55.17% <60.00%> (-1.20%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
done/__init__.py	100.00% <100.00%> (ø)
done/done.py	51.85% <50.00%> (-1.09%)	⬇️

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