Add allowScalingCoefficents option to Chemistry checker

[sjd210]

Moves option for coefficient scaling from content editor to the chemistry checker:

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Main PR here.

[codecov]

Codecov Report

Attention: Patch coverage is 23.07692% with 10 lines in your changes missing coverage. Please review.

Project coverage is 34.17%. Comparing base (95d7ef1) to head (d5161b3).
Report is 30 commits behind head on master.

Files with missing lines	Patch %	Lines
...tg/isaac/quiz/IsaacSymbolicChemistryValidator.java	0.00%	7 Missing ⚠️
.../dtg/isaac/dos/IsaacSymbolicChemistryQuestion.java	33.33%	2 Missing ⚠️
...g/isaac/dto/IsaacSymbolicChemistryQuestionDTO.java	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #646      +/-   ##
==========================================
+ Coverage   34.15%   34.17%   +0.01%     
==========================================
  Files         520      520              
  Lines       23241    23254      +13     
  Branches     2848     2850       +2     
==========================================
+ Hits         7939     7946       +7     
- Misses      14501    14507       +6     
  Partials      801      801              

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[sjd210]

This PR now also allows for certain approved error messages from the Chemistry Checker to be displayed front-end while still being otherwise handled as errors. In this case, we have "Division by zero is undefined!"