Provide a way to rely only on one given main version of Silverpeas

Now, in Debian-based distributions, each main version of Silverpeas will have its own APT repository. In Redhat-based distribution (RHEL and CentOS), each main version of Silverpeas will be provided by a different package name (silverpeas-5.14 for Silverpeas 5.14.x, silverpeas-5.15 for Silverpeas 5.15.x). With this feature, each customer can rely only on a given version of Silverpeas and will have update only for minor versions (bug fixes). To pass to a new main version of Silverpeas can be only done explicitly by the user