I am not sure where the best place for Licenses is but they are not plugins. There is currently no way to add a new license type other than manually adding it to the license table - I have created
MDL-45184 to address that issue.
I do not believe that Licenses belongs in Admin->Plugins->Licenses since it is not really a plugin at all and does not require any code. It is really a site setting and could perhaps go in Admin->Server->Licenses or simple Admin->Licenses. Regardless, I would like to see in removed from Admin->Plugins because there is no Licenses category in Moodle Plugins and I do not envision creating one. Peace - Anthony