Refactor SplitHeader class (#4276)

* Flatten static functions in anonymous namespace

* SplitHeader ctor: Rename param

* Header: Remove unnecessary `virtual`s

* auto ptr where possible

* Add curly braces

* Comment twitch room modes

* Treat roomModes->slowMode as an integer

* Remove unused `this` from lambdas

* Add `unsigned int` overload for localizeNumbers

* Move thumbnail max age to a constexpr static & set explicit types

* Explicitly use `QObject::connect`

* Use `empty()` instead of `size()`

* Name unused parameters

* Move moderation action refreshing logic from SplitHeader to Split

src/widgets/splits/Split.hpp

@@ -130,6 +130,14 @@ private:
      */
     void joinChannelInNewTab(ChannelPtr channel);
 
+    /**
+     * @brief Refresh moderation mode layouts/buttons
+     *
+     * Should be called after after the moderation mode is changed or
+     * moderation actions have been changed
+     **/
+    void refreshModerationMode();
+
     IndirectChannel channel_;
 
     bool moderationMode_{};