Add room upgrades

Fixes #155

lib/helpers/extensions/room_version_at_least.dart

@@ -0,0 +1,8 @@
+extension RoomVersionAtLeast on String? {
+  /// Whether this room version is [version] or newer. Unknown ones, like
+  /// unstable versions, are assumed to be new enough.
+  bool versionAtLeast(int version) => switch (int.tryParse(this ?? "")) {
+    final number? => number >= version,
+    null => true,
+  };
+}