Update the sponsorship level and banner

[adiroiban]

I hope we can get from PSF the list of current sponsors... if any.

And we should update the website.

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We should also define the sponsorship level so that PSF can add them to their accounting tools.

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We should also decide if we still want to keep the sponsorship levels

https://github.com/twisted/trac-wiki-archive/blob/trunk/TwistedSoftwareFoundation.mediawiki#user-content-Sponsorship_Levels

or update them

And create a separate dedicated page on the new website