refactor: Logging (chat logger) (#5058)

It's no longer a singleton

It's now a unique_ptr that dies together with the Application

* Add getChatLogger to EmptyApplication

* unrelated change: Access Application::instance statically

* fix logging init order

* Add changelog entry

mocks/include/mocks/EmptyApplication.hpp

@@ -75,6 +75,12 @@ public:
         return nullptr;
     }
 
+    Logging *getChatLogger() override
+    {
+        assert(!"getChatLogger was called without being initialized");
+        return nullptr;
+    }
+
     ChatterinoBadges *getChatterinoBadges() override
     {
         return nullptr;