POM: rename base POM to pom-ij-base

This avoids a name clash with pom-imagej, which we will now use for an
external common parent POM for all Maven projects in the ImageJ org.
POM: bump to pom-scijava 1.163
POM: remove distributionManagement section

The way to deploy to the ImageJ Maven repository is now by passing
"-Pdeploy-to-imagej" which is inherited from the pom-scijava parent.
POM: remove obsolete comment

The ImageJ repository is no longer included for the pom-scijava parent,
since pom-scijava is now available from Maven Central.
WIP: Make AWT and Swing projects external

See:
* https://github.com/imagej/imagej-ui-awt
* https://github.com/imagej/imagej-ui-swing
* https://github.com/scijava/scijava-ui-awt
* https://github.com/scijava/scijava-ui-swing