Complete the 'Maven NAR' -> 'NAR Maven' renaming

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Change groupId to com.github.maven-nar

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Rename the packages

Since '-' is not a valid part of a package name, we use
com.github.maven.nar instead of com.github.maven-nar.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>