Ability to pass a string of url params

[gitterspec]

Great project. It would be very helpful to have this feature, as passing an encoded preferences string works inconsistently and may also be anti-privacy.

For example, a user can set &theme=simple&safesearch=0 which gets appended to the searx search url.

[demostanis]

Done

[gitterspec]

Awesome - thank you!