POM: bump to latest pom-imagej parent
POM: use Apple stubs present on Maven Central

The problem with com.apple:AppleJavaExtensions:1.5 is that
that artifact is not actually present on Maven Central.
Fortunately, the OrangeExtensions project has an updated
version of the stubs which _is_ available on Maven Central.
POM: remove no-longer-needed ImageJ repository

The only reason we needed the ImageJ repository was for the
AppleJavaExtensions at compile time. With that problem solved,
we can now purge the unused repository reference.
Merge pull request #1 from imagej/pom-updates

POM updates