Add a context menu to rooms in the new room list

The tag options are not implemented out of concern for diff size. 

This splits the context menu classes out to a new "iconized" style which is common across a number of context menus, including the UserMenu.

Some of the badge/sublist styles had to change to better accommodate the menu icon lining up.

This also contains the framework required for https://github.com/vector-im/riot-web/issues/13961

src/i18n/strings/en_EN.json

@@ -1142,6 +1142,11 @@
     "%(count)s unread messages.|one": "1 unread message.",
     "Unread mentions.": "Unread mentions.",
     "Unread messages.": "Unread messages.",
+    "Favourite": "Favourite",
+    "Low Priority": "Low Priority",
+    "Direct Chat": "Direct Chat",
+    "Leave Room": "Leave Room",
+    "Room options": "Room options",
     "Add a topic": "Add a topic",
     "Upgrading this room will shut down the current instance of the room and create an upgraded room with the same name.": "Upgrading this room will shut down the current instance of the room and create an upgraded room with the same name.",
     "This room has already been upgraded.": "This room has already been upgraded.",
@@ -1817,9 +1822,6 @@
     "Mentions only": "Mentions only",
     "Leave": "Leave",
     "Forget": "Forget",
-    "Favourite": "Favourite",
-    "Low Priority": "Low Priority",
-    "Direct Chat": "Direct Chat",
     "Clear status": "Clear status",
     "Update status": "Update status",
     "Set status": "Set status",