Implement Javadoc for....

[rnc]

Missing javadoc for

• MavenMetadataReader (and getMetadata within it)
• MavenXmlView
• MavenPomView
• MavenMetadataView
• Transfer

which are used by https://github.com/release-engineering/pom-manipulation-ext

[jdcasey]

These additional classes are implied.

[jdcasey]

Also Location, in galley-api