Added inverted scroll direction for StackScrollTool

[christianmol]

• Please check if the PR fulfills these requirements

• [x] The commit message follows our guidelines

• [x] Tests for the changes have been added (for bug fixes / features)

• [ ] Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...) Added an option for inverting the scroll direction of the StackScrollTool

• What is the current behavior? (You can also link to an open issue here) StackScrollTool can only scroll in one direction.

• What is the new behavior (if this is a feature change)? By setting the invert option to true, the tool now scrolls the oposite way, like what is possible with the StackScrollWheelTool

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?) No

• Other information:

[codecov[bot]]

Codecov Report

Merging #1535 (37affa2) into master (925a3dd) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1535   +/-   ##
=======================================
  Coverage   21.70%   21.71%           
=======================================
  Files         287      287           
  Lines       10137    10138    +1     
  Branches     2081     2082    +1     
=======================================
+ Hits         2200     2201    +1     
  Misses       6750     6750           
  Partials     1187     1187           

Impacted Files	Coverage Δ
src/tools/StackScrollTool.js	58.82% <100.00%> (+1.24%)	:arrow_up:

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