consistently use "maven" for the maven project type

For the maven project type several names were in use: "maven", "maven2", 
"maven2/3", "maven 2/3".

The 2 and 2/3 variants seem to stem from times when the maven job type
only supported maven 2 while maven 1 still was widely used. 
This is no longer relevant, see
http://maven.apache.org/maven-1.x-eol.html.

I adapted the use of the prominent job pronoun, "maven", which also
reads much better than the 2/3 variants