[fix] Qwant engines - implement API v3 and add 'quant videos'

The implementation uses the Qwant API (https://api.qwant.com/v3). The API is
undocumented but can be reverse engineered by reading the network log of
https://www.qwant.com/

 queries.

This implementation is used by different qwant engines in the settings.yml::

  - name: qwant
    categories: general
    ...
  - name: qwant news
    categories: news
    ...
  - name: qwant images
    categories: images
    ...
  - name: qwant videos
    categories: videos
    ...

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>