Make meetup time prominence configurable

[lukasrad02]

Is your feature request related to a problem? Please describe.
During this semester's Erstitage at HPI, many supporters did not show up on time, since they haven't noticed the dedicated meetup time for their shift. Is is only shown at the details page for the event, not in the event list/calendar (so people might already have decided whether the time is fine for them when selecting an event from the list), is much smaller than the start and end time and has less contrast.

Describe the solution you'd like
Increase the prominence of the meetup time for an event, for example by:

• Showing the meetup time in the events list, too (maybe not on mobile devices/small screens)
• Increasing font size and contrast of the meetup time on the details page of an event
• Adding the meetup time to the exportable calendar (see Use meetup time instead of start time for calendar export #1122)

Describe alternatives you've considered

• Drop the difference between meetup and start time completely and only show one time (might be confusing for users who are already used to the current concept)
• Show a warning/confirmation dialog when signing up for an event with a dedicated meetup time prior to the actual start (very prominent, but also very annoying)

Additional context
This issue is based on the EvaP feedback for the Erstitage at HPI.

[jeriox]

We had a discussion about this and concluded that different types of events warrant different usages of the meetup time (introduction starts at meetup time vs. arrive at some point between meetup and start), so there is no good solutions that fit all usecases.
We agreed on adding a setting on the instance that toggles the meeting time behaviour. If it is set to the "strict" mode, meeting and start times swap places wherever they are used. This is especially true for the shift box (meeting time is the large one, start time is small next to it) and the calendar export (meeting time is iCal start time, see #1122)