message: add hasPlugin method
diff: @@ -21,6 +21,14 @@ struct PluginManager
  // TODO: add functions to get a fresh set of panels, activate/deactive, etc.
  void main(std::shared_ptr<StudioContext> ctx, PanelList *panels = nullptr) const;
  + bool hasPlugin(const std::string &pluginName)
  + {
  + for (auto &p : plugins)
  + if (p.instance->name() == pluginName)
  + return true;
  + return false;
  + }
  +
  private:
  // Helper types //
  struct LoadedPlugin
  