Set maven plugins version numbers.

This avoids the maven warning logs at build time complaining about
lack of version information in maven plugin declarations.
declare all depdendencies in the root pom.

All dependencies that were defined in module specific poms are now defined
in the dependencyManagement section of the root pom, and all dependency
versions are set as properties in the root pom's properties section.

This allows for an easier tracking of dependencies and versions.