Introduce new CMS7 suite releases master pom project

The new CMS7 suite releases master pom will provide dependencyManagement configurations for all those selected artifacts/projects which together represent a specific CMS7 suite release, like 7.5, 7.5.1
The releases of this master pom therefore will correspond one-to-one with, and use the same versioning, as these CMS7 suite releases.

Intended usage of this master pom is as parent pom for custom CMS7 based projects (repository, cms, addons, hst, site) and thereby ensuring the right combination, and supported set, of these artifacts.
If such a custom project wants to upgrade to a newer general release (GA) of CMS7, like going from 7.5 -> 7.5.1, upgrading this master pom version should do the trick, with regards to upgrading to the right set of dependencies.