Add support for the data type 'external identifier' for statements and qualifiers on commons
A external identifier data type is essentially a string with constraints - on wikidata it's entered as a string, but it's validated against the property's constraints (it seems - https://www.wikidata.org/wiki/Property:P269 under constraints)
Users need to be able to add an external id for any property that takes external identifiers as a value, in the File page and in UploadWizard
##Examples
A quantity can be population, maximum capacity, floors above groundAn external identifier can be an IMDB ID, and numeric valuean ISBN, or a Library of Congress authority ID or others (see full list of Wikidata properties that use the quantityexternal identifier data type).
##User storyies
- As a Commons editortor, I want to add an external identifier to a media file’s metadata, I want to add a quantityso that GLAMs can connect this ID to a media file’s metadataother databases for archival purposes.
- As a Commons editor, so that anyone using that file can know a particular kind of quantity pertaining to that fileI want to add an external identifier to a media file’s metadata, including the unit of that quantity (optional)so that other systems can find this Q item by looking up this ID.
##Acceptance criteria:
[] can select a property with data type 'external identifier' and enter a value for it, on File page and UploadWizard
[] on File page
[] in UploadWizard
[] incorrect values return an error
[] add values other than whole and decimal numbers