Feature request: Add personal meetings

[zuphilip]

During a conference one wants to meet with some person(s) besides the official programm. Morevoer, it is possible that there is something like an exhibision of companies and attendees will make appointments with some of them. For these use cases, it would be interesting to have a new feature, which makes it possible to add such personal meetings besides the official programm.

If this would be possible, then the different views should include such personal meetings and they should also taken into consideration when something new will overlapp with the things already saved.

[opk12]

To add another use case for custom events: At SotM 2022, OpenStreetMap's world conference, a lot of on-site self-organized sessions were listed on a physical white board, but not transcribed into the xml schedule. Here are the sessions white board and lightning talks white board.

(PS: You may like that SotM advertises Giggity.)