Advanced channel filters (#1748)

Adds custom channel filters complete with their own mini-language. Filters can be created in settings, and applied by clicking the three dots to open the Split menu and selecting "Set filters".

src/common/WindowDescriptors.hpp

@@ -37,6 +37,8 @@ struct SplitDescriptor {
     // Whether "Moderation Mode" (the sword icon) is enabled in this split or not
     bool moderationMode_{false};
 
+    QList<QUuid> filters_;
+
     static void loadFromJSON(SplitDescriptor &descriptor,
                              const QJsonObject &root, const QJsonObject &data);
 };