GamesSettings: Introduce a new GamesSettings application :^)

This currently has exactly one setting: The background colour for card
games. My thinking is, it's better to not have a Settings application
for each individual game we include in the system, since most will only
have a small number of settings, all Settings windows have tabs anyway,
and I don't want to flood the Settings app list unnecessarily.

As for having a single setting for all the card games: it's nice when
things match. :^)

Userland/Applications/GamesSettings/CMakeLists.txt

@@ -0,0 +1,17 @@
+serenity_component(
+        GamesSettings
+        REQUIRED
+        TARGETS GamesSettings
+)
+
+compile_gml(CardSettingsWidget.gml CardSettingsWidgetGML.h card_settings_widget_gml)
+
+set(SOURCES
+        main.cpp
+        CardSettingsWidgetGML.h
+        CardSettingsWidget.cpp
+        CardSettingsWidget.h
+        )
+
+serenity_app(GamesSettings ICON games)
+target_link_libraries(GamesSettings LibGUI LibMain)