Continue to show meeting on make/meetings while meeting is happening.

[kirasong]

It'd be helpful to be able to confirm that a meeting should happen at a certain time, but right now meetings stop being visible on ​https://make.wordpress.org/meetings the moment they are planned to start, which makes this impossible.

This has been an issue for make/hosting, where there are different times for meetings depending on the week.

I realize there isn't currently data for meeting length to do this in an exact fashion, but It'd be great if the meetings could remain visible for an hour after they start, since that's the standard length for meetings at this point.

[SergeyBiryukov]

In 9038:

Make/Meetings: Show currently ongoing meetings (started no longer than an hour ago) on top of the list.

Props mikeschroder, SergeyBiryukov.
Fixes #4594.

[SergeyBiryukov]

Since [9038], at the end of a meeting it's no longer possible to look when the next one is supposed to be.

Let's keep the current meeting on top of the list for 30 minutes, that should be enough, I think.

[SergeyBiryukov]

In 9078:

Make/Meetings: Reduce the time frame for showing currently ongoing meetings on top of the list from 1 hour to 30 minutes.

Fixes #4594.