Room info bottom sheet

Issue #89.

src/components/roomInfoMixin.js

@@ -0,0 +1,28 @@
+export default {
+  computed: {
+    room() {
+      return this.$matrix.currentRoom;
+    },
+
+    roomName() {
+      if (this.room) {
+        return this.room.name;
+      }
+      return "";
+    },
+
+    roomTopic() {
+      if (this.room) {
+        return this.room.topic;
+      }
+      return "";
+    },
+
+    roomAvatar() {
+      if (this.room) {
+        return this.room.avatar;
+      }
+      return "";
+    },
+  },
+}