Do not try to fetch wikidata ids for links not pointing to articles

[ondenman]

Some articles have links that do not link to files. Since these aren't wikipedia articles, they won't have associated wikidata ids.

Example

When scraping the article for 'cat' for ids, the fetcher logs this warning:
......Can't find Wikidata IDs for: e, Play media, En-Cat (part 1).ogg, En-Cat (part 2).ogg, En-Cat (part 3).ogg in en

Play media is a transport control whilst the latter three links point to sound files.

Fix

Links to files can be filtered out by looking for File: in the URL. For example, the article for Theresa May contains a link to an image of her signature: https://en.wikipedia.org/wiki/File:Signature_of_Theresa_May.svg