POM: use tabs instead of spaces
POM: remove redundant configuration

All of these sections are inherited from the parent.
POM: simplify repositories blocks
POM: use GitHub username for developer ID
POM: fix GitHub Issues URL
POM: use more specific CI URL
POM: fix up dependencies block
POM: remove no-longer-needed configuration blocks

The removed sections have all migrated to the pom-scijava parent.