Support sonatype OSS credentials for uploadArchives.

Support using sonatype OSS credentials or any typical NEXUS server for
uploading the artifacts.
Use prodeps plugin to make logback-classic an optional dependency.

- Use prodeps plugin 0.0.7 to make use of provided and optional
  dependencies
- Mark logback-classic as an optional dependency to avoid making it a
  transitive dependency or being used in the classpath of projects using
  this extension.