Prepare pom.xml for SonaType uploads

* Add a license section.
* Add the necessary scm entries.
* Add the parent entry telling we depend on SonaType's release profile.
* Add (commented) the GPG plugin section.
Script to do a release to SonaType

Usage:

* change the pom.xml so as to remove the -SNAPSHOT out of the version, commit;
* tag (recommended);
* sh dorelease.sh;
* change the pom.xml so that the version is incremented by 1, re-add -SNAPSHOT.