improve handling of EJB-client and other types, according to ArtifactType class

Currently, the artifact deployment code doesn't fully utilize the org.apache.maven.project.ArtifactType class in calculating file names/paths/etc. I propose improving the DefaultArtifactDeployer class to use the ArtifactType appropriate for the specified type in determining the extension for the destination file.

In short, it requires retrieving the ArtifactType enumeration constant which corresponds to the given type string, and extracting the extension from that. If the ArtifactType.findType() method fails, the type parameter passed in is returned as the extension...this all takes place in the DefaultArtifactDeployer.extensionForType() method.

Basically, I'm removing the special case for type="ejb" and using the ArtifactType.findType(type).getExtension() logic instead. If type="ejb", the returned ArtifactType will be equal to ArtifactType.EJB, so all old functionality will be preserved.

I am cross-posting this issue in conjunction with two others: one to modify the maven core to improve dependency-classpath additions based on the ArtifactType class, and another which forms the impetus of this whole effort: to improve the handling of EJB-client jars by the EJB plugin.

The EJB plugin currently generates EJB-client jars in the ${maven.build.dir} and leaves them, without support for installing or deploying them or their snapshot versions. I have fixed this, but only by adding an EJB_CLIENT type to the ArtifactType class, which allows me to use the <artifact:install.../> tags/plugin.

The high level of integration involved with adding support for new artifact types necessitates these three separate patches...I wish it didn't. I will add the other issue ID's to this issue when I have them.

The patch for this improvement is attached.