Why can't we be friends

Update the UX to refer to structure direct chats as friends. The direct chats are pulled into their own tab in the space drawer.

The `UserDetailDialog` is also updated to check whether a direct chat already exists and if not ask to invite as friend.

![image](/uploads/67f13fa8558e704e0acaf7c60e135bbc/image.png)

src/models/roomlistmodel.h

@@ -77,6 +77,7 @@ public:
         IsSpaceRole, /**< Whether the room is a space. */
         IsChildSpaceRole, /**< Whether this space is a child of a different space. */
         ReplacementIdRole, /**< The room id of the room replacing this one, if any. */
+        IsDirectChat, /**< Whether this room is a direct chat. */
     };
     Q_ENUM(EventRoles)