Upgraded OpenTTD and OpenGFX to their latest versions

Upgraded to the latest version of OpenTTD, an open source implementation of the classic Transport Tycoon Deluxe game.

  * OpenTTD upgraded to version 1.3.0
  * The supporting graphics library, OpenGFX upgraded to version 0.4.6.1

Other than that: Nothing changed from the formular that installed the 1.2.3 version