POM: fix order of GAV elements
POM: bump to pom-fiji 5.0

This updates to the latest SciJava software components.

It also uses release versions for all Fiji components.
POM: use public group for ImageJ repositories

This is better for a variety of reasons:
* Covers both releases and snapshots.
* Covers other repositories including thirdparty.
* Supports artifacts being reorganized in the future.
* Avoids future POM edits in case additional repositories are needed.
POM: tidy up order of configuration blocks

Accomplished using:
    mvn tidy:pom
POM: bump to pom-fiji 5.0.2
Merge pull request #7 from ctrueden/pom-updates

POM updates