Tidy up headings on event series

[jennpb]

What?

Event series pages organise the upcoming and past events using h2 headings. The way they're currently phrased is more conversational rather than useful for navigable headings. I suggest changing to the proposed labels, pending review by @dannybirchall

State	Now	Proposed
Scheduled events	What's next	Coming up
No scheduled events	No events scheduled at the moment, check back soon...	No upcoming events
Events in past	What we've done before	Past events

Example https://wellcomecollection.org/event-series/WoK-NioAACkANeWK

Why?

• Greater applicability to all states
• Makes text more scannable
• Plain language

Background

This is a legacy holdover from our first design iteration.

Done when

• [x] Danny gives the ok or suggests alternatives
• [x] Headings changed for each state

[dannybirchall]

yes, this makes sense to me!