Test and leverage Maven 3.3

Maven 3.3.1 comes with some very interesting improvements.
Test and leverage their use in Nuxeo.
For instance:

• root directory
• extensions
• toolchains

http://blog.soebes.de/blog/2015/03/17/apache-maven-3-dot-3-1-features/
https://jira.codehaus.org/secure/ReleaseNote.jspa?projectId=10500&version=21013
http://maven.apache.org/guides/mini/guide-using-toolchains.html
https://jira.codehaus.org/browse/MNG-5771
https://jira.codehaus.org/browse/MNG-5786
https://git-wip-us.apache.org/repos/asf?p=maven.git;a=blobdiff;f=apache-maven/src/bin/mvn;h=26feda4218197811e95390b746e2e002b585dd3b;hp=1ed3024b3fe442dc1e95fef193661abcde298a19;hb=8ed9a1caa8890773b45c6c408a4e40acf4f4b0fd;hpb=ee7dbab69dd87d219031b0715105527cdbf12639