add metadata fields to /location-units/campuses endpoints

The change metadata property is now called metadata (no capital d).

I think the latest RAML module builder version relies on this ( correct me if this is wrong). The change metadata in mod-circulation-storage and mod-circulation is still kept in the metaData property as they were the first to introduce it, before the change in name, and it would be a breaking change and so needs scheduling in (and also blocks upgrading the RAML module builder in mod-circulation-storage).

I've change the issue title and description.