Remove dependency on publishing plugin

Circular dependency between two plugins: `gradle-publishing-plugin` <-> `gradle-contacts-plugin`

* `nebula.plugin.publishing.maven.PomDevelopersPlugin` needs `nebula.plugin.contacts.BaseContactsPlugin`
* `nebula.plugin.contacts.PomDevelopersPlugin` needs `nebula.plugin.publishing.maven.NebulaBaseMavenPublishingPlugin`