Figures bug fixes

[johnbaldwin]

• Addresses progress data pipeline errors in LearnerCourseDetails serializer
  • https://github.com/appsembler/figures/issues/217
  • Added testing for LearnerCourseGradeMetricsManager
  • Updates LearnerCourseDetailsSerializer.get_prgress_data check if there is not a record to process
  • Adds serializer testing for the above
• Fixes Ginkgo migration for a Django 1.8 -> 1.11 incompatibility

[melvinsoft]

@johnbaldwin I'll review this one today.

[codecov-io]

Codecov Report

Merging #213 into master will decrease coverage by 0.18%. The diff coverage is 88.88%.

@@            Coverage Diff             @@
##           master     #213      +/-   ##
==========================================
- Coverage   91.31%   91.12%   -0.19%     
==========================================
  Files          37       37              
  Lines        1876     1882       +6     
==========================================
+ Hits         1713     1715       +2     
- Misses        163      167       +4     

Impacted Files	Coverage Δ
figures/migrations/0010_site_monthly_metrics.py	90.90% <75.00%> (-9.10%)	:arrow_down:
figures/serializers.py	94.37% <100.00%> (-1.16%)	:arrow_down:

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