add remote capability to facilitate a 2.x to 3.x upgrade

The upgrade procedure from repository manager 2.x to 3.x requires an special capability to manage the upgrade process on the version 2.x side. The protocols implemented by this will be used by an upgrade process driven by the version 3.x instance being upgraded into.

Nexus Repository Manager 2.14 is the first release containing the capability to upgrade to Nexus 3.1 and greater.