Add support for additional search engines

[mrose17]

for "parity' with the mobile browsers, we should add: Bing, Yahoo, Amazon.com, Twitter, and Wikipedia.

#3053

[psimyn]

I was working on this for #466 (example near the bottom)

Still needs UI fixes and preferences page added though

[mrose17]

most excellent!

[ghost]

Is it possible to add qwant.com too ?

[LoloIrie]

Qwant would be nice +1

[Superbest]

I would also suggest:

• A searx instance such as searx.me
• startpage.com and/or ixquick

[luixxiul]

@bbondy is it worth considering or under consideration to implement OpenSearch?

[bbondy]

we do parse OpenSearch for Google and DuckDuck go. I think we can just do a simple big list like this in preferences though, I think there's a mockup in one of the preferences issues.

[bsclifton]

+1 from support for IxQuick/StartPage

[kskarthik]

Please also add searx.me meta search engine. cc: @asciimoo

[mrose17]

OBE

[Ornataweaver]

#790 #824 #3053 #3294 #4210

[jeroenev]

please add search.gibberfish.org as searx.me alternative, it's hosted by a non polrofit organization, searx.me seems to be overloaded, not to mention gets it's results from.german versions of.search engines, gibberfish gets.them from american versions