Adapt POMs for deploying at Maven Central (#713).

For deploying (a snapshot) at Maven Central:
{{{
mvn clean deploy -P release
}}}
Executable from DM home.

Changes:
* The `release` profile defines all modules to be deployed.
* Moved <distributionManagement> from Parent POM to Global POM.
* Set Global POM as the parent for both
    * Parent POM
    * Plugin Parent POM

See #713.