Modifications to support proper build of FreeCol as a Mac application bundle

[DonWaugaman]

Modifications to support proper build of FreeCol as a Mac application bundle.

• Delete the old "FreeCol" executable
• Add the universalJavaApplicationStub (from https://github.com/tofi86/universalJavaApplicationStub). MIT licensed. With the jarbundler ANT task, allows Java applications to be started with whatever JDK/JRE is available on the system. Apple's solution won't work for Java 1.8 and above.
• Change build.xml to start up net.sf.freecol.FreeCol as the main class. Added a property to the file so that the main class name stays consistent between Mac app bundles and the manifest file for PC builds.

Without this, a user who unpacks the app bundle in /Applications and then clicks on the FreeCol icon will get a dialog saying that the bundle is damaged or cannot be executed. With these changes, it starts correctly. I've tested this on Mac OS 10.11, 10.14 and 10.15.

However, when a brand new FreeCol user starts up the app, it will close itself immediately with no error message displayed. This happens because the freecol per-user directory under ~/Library/Preferences hasn't been created. You can see this if you invoke the universalJavaApplicationStub directly; e.g. calvin[bash]~ -> /Applications/FreeCol.app/Contents/MacOS/universalJavaApplicationStub Bad user configuration directory: /Users/dpw/Library/Preferences/freecol

A workaround is to create it by hand: mkdir ~/Library/Preferences/freecol but the application really needs to create this directory for the user if it does not yet exist.

A similar subdirectory, ~/Library/Application Support/freecol, is created if it does not yet exist. Would it be possible to add code to create the subdirectory under Preferences in the same way?

[mpope042]

Looks good, at least as far as I can tell without a mac. Merged in git.182376b.