dynamically generate splash window from version

Now, the JESsplash.png file is blank. There's a new JESSplashWindow
class that loads that file, writes the current version information
on it, and then displays the splash screen. It gets the version
information from the JESVersion class.
dynamically replace version in JESIntroduction

The token @version@ is replaced with the current version (like "5.0",
not "5.0-snapshot" or whatever).
allow release number to be selected in Ant

Now, Ant normally builds -snapshot releases. To build final releases,
add a "-Drelease=" parameter, or "-Drelease=a1" for some other type of
release.