Better intergrating of private meetings

[LenaWil]

Now that #304 is finally live, I discovered a couple of things I want:

• [ ] Meetings aren’t shown on the activity page.
• [ ] The main activity page if you made one is hard to find.
• [ ] Todo: find out how the pages work with less permissions.
• [ ] Give more edit permission to people.
• [ ] Enable it for all people.