add(pydeck) support for deck.gl widgets

[chrisgervang]

For #9056

Background

Adds support for deck.gl widgets in pydeck.

Note: This cannot be throughly tested until the changes to @deck.gl/jupyter-widget are released.

Change List

• add a Widget binding to pydeck
• bundles widgets from @deck.gl/widgets
• intro example
• docs

[coveralls]

coverage: 91.675%. remained the same
when pulling c70846f on chr/pydeck-widgets
into 47b62e0 on master.

[coveralls]

coverage: 91.675%. remained the same
when pulling 3b4943d on chr/pydeck-widgets
into 2ba7157 on master.

[felixpalmer]

Note: This cannot be throughly tested until the changes to @deck.gl/jupyter-widget are released.
@chrisgervang would a beta of deck.gl 9.1 with this PR included be sufficient?

[chrisgervang]

@felixpalmer yup, that's what I'm thinking