DS-4107 Retrieve and model metadata as a map

.../modify-item-overview/modify-item-overview.component.html

...ge/modify-item-overview/modify-item-overview.component.ts

...ts/metadata-uri-values/metadata-uri-values.component.html

...ents/metadata-uri-values/metadata-uri-values.component.ts

...components/metadata-values/metadata-values.component.html

...d-components/metadata-values/metadata-values.component.ts

...-components/file-section/full-file-section.component.html

src/app/+item-page/full/full-item-page.component.html

src/app/+item-page/full/full-item-page.component.ts

...ts/specific-field/item-page-specific-field.component.html

...specific-field/title/item-page-title-field.component.html

...nts/specific-field/uri/item-page-uri-field.component.html

src/app/+search-page/normalized-search-result.model.ts

src/app/+search-page/search-result.model.ts

src/app/core/browse/browse.service.ts

src/app/core/cache/models/normalized-dspace-object.model.ts

src/app/core/data/search-response-parsing.service.ts

src/app/core/dspace-rest-v2/dspace-rest-v2.service.ts

src/app/core/metadata/metadata.service.ts

src/app/core/shared/collection.model.ts