Prevent leaving from specific groups

[turt2live]

Description

For cases such as workplaces, an overarching admin should be able to define specific groups as manual membership, including the prevention of leaving. This would be for +developers:company.com or +support:company.com, where employees aren't allowed to say they aren't part of a department (logically).

However, there still needs to be a way for people to be removed (people quit, get fired, transferred, etc).

This should prevent FFA groups, as described in #5242. A group should either be 'forced membership', 'ffa', or 'default' (current behaviour). Not any combination of the 3.

Version information

• Platform: web (in-browser)
• Browser: Chrome 61
• OS: Windows 10
• URL: riot.im/develop

[lampholder]

I think this is an absolutely key feature for groups.

[turt2live]

Closing because its from the groups era. If someone wants this for spaces, please open a new issue.