Add viewer capabality to workflow widget

[TimMonko]

• Adds a separate tab for viewer capabilities
• Select roots from the list of layers in napari
• Yield each task from the workflow into a napari layer
• Update the progress bar for each task
• Adds full test coverage

closes #151

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.29%. Comparing base (8782857) to head (1aa4a1b).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #156      +/-   ##
==========================================
+ Coverage   85.82%   86.29%   +0.47%     
==========================================
  Files          32       32              
  Lines        2723     2817      +94     
  Branches      193      201       +8     
==========================================
+ Hits         2337     2431      +94     
  Misses        328      328              
  Partials       58       58              

Flag	Coverage Δ
unittests	86.29% <100.00%> (+0.47%)	⬆️

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