Add: create bundles via CPack

CPack works closely together with CMake to do the right thing in
terms of bundling (called 'package'). This generates all the
packaging we need, and some more.

cmake/PackageBundle.cmake

@@ -0,0 +1,24 @@
+string(TIMESTAMP CURRENT_YEAR "%Y")
+
+set(CPACK_BUNDLE_NAME "OpenTTD")
+set(CPACK_BUNDLE_ICON "${CMAKE_SOURCE_DIR}/os/macosx/openttd.icns")
+set(CPACK_BUNDLE_PLIST "${CMAKE_CURRENT_BINARY_DIR}/Info.plist")
+set(CPACK_BUNDLE_STARTUP_COMMAND "${CMAKE_SOURCE_DIR}/os/macosx/launch.sh")
+set(CPACK_DMG_BACKGROUND_IMAGE "${CMAKE_SOURCE_DIR}/os/macosx/splash.png")
+
+# Create a temporary Info.plist.in, where we will fill in the version via
+# CPackProperties.cmake.in. This because at this point in time the version
+# is not yet known.
+configure_file("${CMAKE_SOURCE_DIR}/os/macosx/Info.plist.in" "${CMAKE_CURRENT_BINARY_DIR}/Info.plist.in")
+set(CPACK_BUNDLE_PLIST_SOURCE "${CMAKE_CURRENT_BINARY_DIR}/Info.plist.in")
+
+# Delay fixup_bundle() till the install step; this makes sure all executables
+# exists and it can do its job.
+install(
+    CODE
+    "
+        include(BundleUtilities)
+        fixup_bundle(\"\${CMAKE_INSTALL_PREFIX}/openttd\"  \"\" \"\")
+    "
+    DESTINATION .
+    COMPONENT Runtime)