The identifier modal should make an educated guess when pasting URLs.

This should be achievable with the use of more elaborate regular expressions.

If pasted a URL, it should be pretty straightforward to extract the identifier

1. Example: https://www.wikidata.org/wiki/Q150827
2. Current regexp:

   ^Q\d+$
   

1. Proposed regexp:

   ^(?:(?:(https?):\/\/)?(?:www\.)?wikidata\.org\/wiki\/)?Q\d+$
   

1. This will match http://www.… and https://www… and also wikidata.org/… and also the identifier by itself