Move GPU.js to devDependencies and add it to optionalDependencies.

[jansiegel]

Context

Remove gpu.js from dependencies and it to devDependencies and optionalDependencies.

This can be considered as a breaking change, as it will no longer be installed by default.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature or improvement (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Additional language file or change to the existing one (translations)

Related issue(s):

1. gpu.js is listed as required dependency #642

Checklist:

• My code follows the code style of this project,
• My change requires a change to the documentation,
• I described the modification in the CHANGELOG.md file.

[codecov]

Codecov Report

Merging #644 (6ca400f) into develop (543b3ff) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #644   +/-   ##
========================================
  Coverage    92.49%   92.49%           
========================================
  Files          164      164           
  Lines        38486    38486           
  Branches      5340     5340           
========================================
  Hits         35596    35596           
- Misses        2853     2884   +31     
+ Partials        37        6   -31     

Impacted Files	Coverage Δ
src/Cell.ts	95.50% <0.00%> (ø)
src/Operations.ts	91.15% <0.00%> (ø)
src/DateTimeHelper.ts	82.62% <0.00%> (ø)
src/DateTimeDefault.ts	56.36% <0.00%> (ø)
src/AbsoluteCellRange.ts	86.93% <0.00%> (ø)
src/Lookup/AdvancedFind.ts	92.00% <0.00%> (ø)
src/parser/FormulaParser.ts	81.61% <0.00%> (ø)
src/interpreter/Criterion.ts	84.40% <0.00%> (ø)
src/interpreter/binarySearch.ts	74.72% <0.00%> (ø)
src/interpreter/ArithmeticHelper.ts	83.66% <0.00%> (ø)
... and 9 more