WIP: GroupchatControl: Add group chat info popover and display JID in banner
This adds a second label to show the group chat's name and the JID.
Additionally, the avatar is sized like in the single chat window.
The subject popover is replaced by a room info popover displaying the following group chat infos:
- Title
- JID
- Description
- Subject
- Access
- Password protection
- Anonymity
- Persistence
- MAM
- Language
This depends on !459 (merged).