Add layers visualization

[jeremypuchta]

Add layers visualization. The visualization provides insights in the software architecture, specifically whether there are invalid dependencies between layers of a software system. It can be used if the graph contains nodes that are assigned to nodes with the :Layer property. Nodes with :Layer property should have and the :DEFINES_DEPENDENCY relationship to find (in-)valid dependencies.

[codecov]

Codecov Report

Merging #38 into development will decrease coverage by 3.48%.
The diff coverage is 3.49%.

@@               Coverage Diff               @@
##           development      #38      +/-   ##
===============================================
- Coverage        44.06%   40.58%   -3.49%     
===============================================
  Files               44       47       +3     
  Lines             1475     1604     +129     
  Branches           200      220      +20     
===============================================
+ Hits               650      651       +1     
- Misses             720      828     +108     
- Partials           105      125      +20     

Impacted Files	Coverage Δ
src/api/models/Hotspots.js	25.00% <ø> (ø)
src/api/models/LayersModel.js	0.00% <0.00%> (ø)
...iews/Dashboard/Architecture/Layers/CustomHeader.js	0.00% <0.00%> (ø)
src/views/Dashboard/Architecture/Layers/Layers.js	0.00% <0.00%> (ø)
src/routes.js	57.69% <21.42%> (-0.65%)	⬇️
src/api/models/Dashboard.js	31.76% <100.00%> (ø)
src/api/models/Dependencies.js	32.14% <100.00%> (ø)

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[naraesk]

Thanks, great work.
@rmllr: Can be merged in my view.