basic working export of marking data

[struan]

this is unweighted but does handle raw and percentage marks

[codecov-commenter]

Codecov Report

Merging #99 (281926c) into main (a54ee4b) will increase coverage by 1.52%.
The diff coverage is 96.55%.

@@            Coverage Diff             @@
##             main      #99      +/-   ##
==========================================
+ Coverage   74.74%   76.26%   +1.52%     
==========================================
  Files          54       56       +2     
  Lines        2249     2423     +174     
  Branches      217      229      +12     
==========================================
+ Hits         1681     1848     +167     
- Misses        515      521       +6     
- Partials       53       54       +1     

Impacted Files	Coverage Δ
crowdsourcer/management/commands/export_marks.py	91.66% <91.66%> (ø)
crowdsourcer/tests/test_export.py	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

[struan]

This has been merged