add ipywidgets dependency

[AurelienBoland]

This dependency is necessary for the progress bar

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.37%. Comparing base (46fc0e5) to head (789e786).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #241   +/-   ##
=======================================
  Coverage   91.37%   91.37%           
=======================================
  Files          12       12           
  Lines         580      580           
=======================================
  Hits          530      530           
  Misses         50       50           

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[nalepae]

Only if you use a notebook:
https://nalepae.github.io/pandarallel/troubleshooting/

We should not add this dependancies for users using pandarallel outside of notebook.
An other idea would be to add an "extra" containing ipywidget