Move mocks to their own interface (#4645)

mocks/include/mocks/EmptyApplication.hpp

@@ -0,0 +1,81 @@
+#pragma once
+
+#include "Application.hpp"
+
+namespace chatterino::mock {
+
+class EmptyApplication : public IApplication
+{
+public:
+    Theme *getThemes() override
+    {
+        return nullptr;
+    }
+
+    Fonts *getFonts() override
+    {
+        return nullptr;
+    }
+
+    IEmotes *getEmotes() override
+    {
+        return nullptr;
+    }
+
+    AccountController *getAccounts() override
+    {
+        return nullptr;
+    }
+
+    HotkeyController *getHotkeys() override
+    {
+        return nullptr;
+    }
+
+    WindowManager *getWindows() override
+    {
+        return nullptr;
+    }
+
+    Toasts *getToasts() override
+    {
+        return nullptr;
+    }
+
+    CommandController *getCommands() override
+    {
+        return nullptr;
+    }
+
+    NotificationController *getNotifications() override
+    {
+        return nullptr;
+    }
+
+    HighlightController *getHighlights() override
+    {
+        return nullptr;
+    }
+
+    TwitchIrcServer *getTwitch() override
+    {
+        return nullptr;
+    }
+
+    ChatterinoBadges *getChatterinoBadges() override
+    {
+        return nullptr;
+    }
+
+    FfzBadges *getFfzBadges() override
+    {
+        return nullptr;
+    }
+
+    IUserDataController *getUserData() override
+    {
+        return nullptr;
+    }
+};
+
+}  // namespace chatterino::mock