core: modified filters for selectors

[seeyabye]

This is a follow-up on #11907

This PR moves filters in to be defined individually for each selector.

Example code:

  selectors:
    - selector: a[href^="download.php?id="]
      attribute: href
      filters:
        - name: querystring
          args: url
        - name: urldecode
    - selector: a[href^="magnet:"]
      filters:
        - name: tolower

The first selector's filter will apply querystring and urldecode. The second selector's filter will apply tolower

[ilike2burnthing]

tested, working