Document location shows display name of path

The document location will render the last path element of the root folder plus all path elements of the default path, separated by slashes. Each path element should be the display name, as shown in the CMS (which may differ from the node names in the 'actual' JCR path).

Add a REST API to translate a JCR path to its display name and use this in the frontend to get and show the display name for the 'location' field.

Example: when the rootPath is 'stuff/products' and the default path is '2016/summer-sale', the display name of the path could be 'Products/2016/Summer Sale'. If the defaultPath is empty, only the last element of the root path is shown. If the root path is empty, the last element of the Channel's content root is shown.

Also make the API return the locale of the last folder in the path. This locale is needed to generate the right URL (which may be locale-specific). This also means that when another folder is selected, and the locale of the folder differs from the previous one, the auto-generated URL of the document needs to be re-generated because there might be a locale-specific way to generate the URL of that locale.