[#350] improved prediction by averaging fact values

[Samuel-Campbell]

1) created a binary dictionary of average vector per regressor 2) Regressor initiates all 0 values to their mean column value before making a prediction 3) fact values greater than 0 are kept as such 4) prediction makes more sense given that not all questions are always asked.

[codecov[bot]]

Codecov Report

Merging #360 into master will decrease coverage by 0.32%. The diff coverage is 11.76%.

@@            Coverage Diff             @@
##           master     #360      +/-   ##
==========================================
- Coverage   68.65%   68.33%   -0.33%     
==========================================
  Files          51       51              
  Lines        2013     2021       +8     
  Branches       16       16              
==========================================
- Hits         1382     1381       -1     
- Misses        629      638       +9     
  Partials        2        2

Impacted Files	Coverage Δ
...regression/multi_output/multi_output_regression.py	55.17% <33.33%> (+3.65%)	:arrow_up:
...ion/single_output_regression/abstract_regressor.py	28.12% <7.14%> (-6.5%)	:arrow_down:

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