Description

In the About widget we generalize the concept of Metadata which are Name/Labels, Descriptions and Aliases of a given ZPersistentObject.
Each of those metadata items are associated to a language, which we use for searching, filtering and rendering the About widget.

A bunch of methods return either single Metadata objects or arrays of Metadata. Each Metadata object contains the following properties:

* langIsoCode
* langZid
* rowId

Follow the same ideas as with store/classes/LabelData or store/classes/Row and create a Metadata type to use in all these methods.

Completion checklist

• Before closing this task, review one by one the checklist available here: https://www.mediawiki.org/wiki/Abstract_Wikipedia_team/Definition_of_Done#Front-end_Task/Bug_Completion_Checklist