consistently use "maven" for the maven project type

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

Since maven 1 was deprecated such a long time ago
(http://maven.apache.org/maven-1.x-eol.html), still indicating that this
version is not supported by the maven project type is likely to cause
confusion.

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