[doc] Normalize docblock of interface

Normalize a docblock of UrlRepositoryInterface according to the JsonUrlRepository implementation by adding the @throws tag.
Update signature of `find()` method

`UrlRepositoryInterface::find()` will have to handle a second, optional argument in order to get the values to fill placeholders in.
[refactor] Rename variable
Handle placeholders in URLs

This adds the ability to extract and replace placeholders in URL patterns.
Update doc provider to transfer placeholder values

The DocumentProvider now allows to pass placeholder values to the underlying URL repository.
Merge branch 'refs/heads/handle-patterns-in-urlrepository'
Add MP list URL pattern for specific legislature

This URL pattern allows to specify a legislature number in order to get the corresponding list of MPs.
Add ability to scrape old MP lists

The `scrape()` method now accepts an optional argument to specify the number of the legislature from which the list of MP has to be scraped.

Lists of previous legislatures contain much less data than the list of the current one.