Revise group clear/leave/delete behavior

[lgrahl]

Expected Behavior

If I delete the group, it should be deleted and the conversation should be removed as well.

Current Behavior

The group is being disbanded (everyone is being kicked from the group, including me) but the conversation remains.

[dbrgn]

Definitely! That's a long-standing issue (the current behavior mirrored the delete button in the Android app), now that the behavior has been improved in the app we should provide the same buttons:

• Empty chat
• Leave group
• Delete group

When deleting a group, appropriate warnings should be shown (they might be different depending on whether you're the admin or not).

[mimiks]

Note that the confirmation dialogs for "leave" and "delete" are different in the app depending on if you're a group administrator or not.