Ports: Create launchers for the stpuzzles port

This changes the .port_include.sh script so that ports can more easily
create more than one launcher by making the install_launcher function
available to the port's package.sh script.

This creates launchers for the stpuzzles port in the Games/Puzzles
category.

Ports/cmatrix/package.sh

@@ -17,5 +17,4 @@ configure() {
 
 install() {
     run cp cmatrix "${SERENITY_INSTALL_ROOT}/bin"
-    install_launcher
 }