feat(timepicker): Updated timepicker component to bootstrap 4

[nagos]

• read and followed the CONTRIBUTING.md guide.
• built and tested the changes locally.
• added/updated tests.
• added/updated API documentation.
• added/updated demos.

Bootstrap 4 removed .hidden class.
bootstrap migration guide

The .hidden and .show classes have been removed because they conflicted with jQuery’s $(...).hide() and $(...).show() methods. Instead, try toggling the [hidden] attribute or use inline styles like style="display: none;" and style="display: block;".

[codecov]

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@@              Coverage Diff               @@
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  Files                  ?      254           
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  Hits                   ?     5976           
  Misses                 ?     1868           
  Partials               ?      422

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[valorkin]

thanks for your PR!
sorry for the delay, was busy organizing https://ngtalks.io/