Update event key to use meetup uid to ensure there are no duplicate events (#675)

* Update event key to use meetup uid to ensure there are no duplicate events. Add tests to check this

* Fix tests by passing a MeetupEvent object for upcoming_events

* Add note about how to run tests to README

* Update script to read and replace all Meetup Events to ensure that the event titles and descriptions are up-to-date

* Update tools/meetup_import.py to remove try-catch block and instead revert to empty string

Co-authored-by: Airah✨ <airahyusuff@gmail.com>

* Remove events from events.yml with title-date uid duplicates
Running the script again `sh meetup_event.sh` now does not generate any further duplicates

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Co-authored-by: Silke Nodwell <silke.nodwell17@imperial.ac.uk>
Co-authored-by: Airah✨ <airahyusuff@gmail.com>

Author: 3 people