Is your feature request related to a problem? Please describe.
It is not uncommon to join multiple related MUCs on a separate MUC component URL, like for example all the joinjabber.org chat rooms. It would be nice to have them sorted all together in the control-box under a common header.

Describe the solution you'd like
Similar to roster-groups, there could be collapsible group headers for the components, named after the muc-component name.
The header should probably only be visible if there are 3 or more MUCs under the same component address.

In addition it would be interesting to have an "add all" button on the join MUC dialog after discovering the available MUCs of a muc-component to quickly join an entire "space" of related public MUCs.

Additional context
Despite not really used for such, muc-components could be used as a way to group mucs similar to how other chat systems do it with so called "spaces" or "guilds/servers". The backend is already there, but no client implements an UI for it.