Switch to using Meetup's GraphQL API

[davidfischer]

Meetup.com has a new GraphQL API to replace their REST API that we were previously using to display upcoming events on our website. Meetup's documentation and landing pages seem to point to this new API requiring a Meetup.com PRO subscription (paid). We were able to get an API key as part of the Python Software Foundation's "Meetup Pro Network". However, in testing, I was able to query the API without authenticating whatsoever.

Just a few notes:

• Meetup's documentation does not appear to be 100% accurate. I found a few fields in their field reference that were not correct.
• The API Playground does appear to be accurate and is very helpful for testing the API.
• I found that I did not need an API key simply for simple querying. Their authorization is using OAuth and most of the use cases are for authorizing attendees rather than simply querying data from Meetup.

Ref: #182