New engine: Bing videos

[mod] upgrade dependencies

Mostly interresting for :
* pyopenssl : https://github.com/pyca/pyopenssl/pull/578
* certifi

Avoid UnicodeEncodeError when redirecting standalone output

This modification allows us to deactivate engines in settings.yml
without commenting them out

show engine errors in infobox && add new error alert

long suggestions now wrap around the box instead of going overboard.

fix github url

[fix] fix xpath of google images

[fix] fix duckduckgo's offset

First page now starts with 0 offset,
rather than starting on the 30th result.

DuckDuckGo returns 30 results on each page.

Update translations

Add free software directory engine

[mod] the static and templates directories can be defined in the settings.yml