RE-1933 adding the buildnumber plugin and filtering the "./version/" dir...

...ectory in any artifact to keep backwards compatibility with what we used to have with the subversion revision number plugin

Recommended contents of the ./version/ directory is an XML file named after the artifact that contains it (to de-conflict with other foo-version.xml file on the classpath in a WAR) like this:

    =====  Example filtered file for artifact "foo" =====
    version/foo-version.xml
    =====================================================
     <?xml version="1.0" encoding="UTF-8"?>
     <root>
         <project.artifactId>${project.artifactId}</project.artifactId>
         <project.version>${project.version}</project.version>
         <build.number>${buildNumber}</build.number>
         <build.timestamp>${timestamp}</build.timestamp>
     </root>