Add ability to disable or enable safesearch on Qwant web & image search

[Krando]

Is your feature request related to a problem? Please describe.
Searxng has so far not implemented safesearch on it's Qwant module yet but this can be easily done using the 's' parameter.

Describe the solution you'd like
For any search on it's web or image section, simply attach &s=0 to disable safesearch, &s=1 to enable moderate safesearch or &s=2 to enable strict safesearch.

This is with strict safesearch:

https://www.qwant.com/?s=2&q=dead+lion&t=images&s=2

This is with no safesearch:

https://www.qwant.com/?s=2&q=dead+lion&t=images&s=0

Describe alternatives you've considered

Additional context

[return42]

@Krando thanks for pointing out / I send #1652 would you give it a try?

FWIW: we use the API https://api.qwant.com/v3 .. the safesearch argument in the API is: &safesearch=