Support Icons

[clarasb]

This PR adds icon support for the Button, IconButton and Tabs components by,

• adding an Iconcomponent with the property iconName. iconName has to be a string that corresponds with the names of the Material Icons. For the component the fontFamiliy is set to Material Icons
• integrating the Icon component into Button, IconButton and Tabs

Other changes:

• in chartlets.py/chartlets/components/button.py: Added size and removed variant property from IconButton
  component to align with component in chartlets.js.
• in chartlets.js/packages/demo/packages.json added "@fontsource/material-icons": "^5.1.1" to devDependencies to make icons available in Demo

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.22%. Comparing base (c707e53) to head (577b134).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #138   +/-   ##
=======================================
  Coverage   92.21%   92.22%           
=======================================
  Files          86       87    +1     
  Lines        1503     1504    +1     
  Branches      231      231           
=======================================
+ Hits         1386     1387    +1     
  Misses         98       98           
  Partials       19       19           

Flag	Coverage Δ
backend	100.00% <100.00%> (ø)
frontend	83.92% <100.00%> (+0.02%)	⬆️

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