Fix group of CapabilitiesPlugin

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>
Move CapabilitiesPlugin to org.sonatype.nexus.capability (similar to other plugins)

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>
Use artifact/group ids from CapabilitiesPlugin

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>