"Private chat" header for direct chats

Also, auto-create account and room when joining a DM chat link.

src/components/roomInfoMixin.js

@@ -82,6 +82,23 @@ export default {
       return isAdmin;
     },
 
+    isPrivate() {
+      return this.$matrix.isDirectRoom(this.room);
+    },
+
+    /**
+     * If this is a direct chat with someone, return that member here.
+     * @returns MXMember of the one we are chatting with, or 'undefined'.
+     */
+    privateParty() {
+      if (this.isPrivate) {
+        const membersButMe = this.room.getMembers().filter(m => m.userId != this.$matrix.currentUserId);
+        if (membersButMe.length == 1) {
+          return membersButMe[0];
+        }
+      }
+      return undefined;
+    },
   },
   watch: {
     room: {
@@ -165,5 +182,19 @@ export default {
         this.updatePermissions();
       }
     },
+
+    privatePartyAvatar(size) {
+      const other = this.privateParty;
+      if (other) {
+        return other.getAvatarUrl(
+          this.$matrix.matrixClient.getHomeserverUrl(),
+          size,
+          size,
+          "scale",
+          true
+        );
+      }
+      return undefined;
+    },
   },
 }