Add support for fullscreen mode

Add support for toggle in "RuneLite" settings to go into fullscreen
mode, that will make RuneLite window fully fullscreen without any weird
hacks.

Signed-off-by: Tomas Slusny <slusnucky@gmail.com>

runelite-client/src/main/java/net/runelite/client/config/RuneLiteConfig.java

@@ -112,6 +112,18 @@ public interface RuneLiteConfig extends Config
 		return false;
 	}
 
+	@ConfigItem(
+		keyName = "fullscreen",
+		name = "Fullscreen mode",
+		description = "Switch window to fullscreen mode.",
+		warning = "Please restart your client after changing this setting",
+		position = 17
+	)
+	default boolean enableFullscreen()
+	{
+		return false;
+	}
+
 	@ConfigItem(
 		keyName = "notificationTray",
 		name = "Enable tray notifications",