Tracker: Python documentation improvements

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Examples

• Full screen button (and deck.gl docs) buttons are below the code. Full screen button should be directly below the live example.
• deck.gl / pydeck attribution widget - This is a general issue. Right now, especially the full screen examples have two mapbox attributions, which is very misleading.

TOC

• main page should be listed within ToC. Right now I have to click on top pydeck title.

Footer

• Copyright notice and sphinx build note do not add much and are inconsistent with the rest of our docs.

Front page

• Add a section with contributing companies (Uber/Unfolded etc).

[ibgreen]

@kashuk Please add items based on your review of the pydeck.gl site.