Fix results with no scheme

Related to #428, which was fixed in e3df22b but broken in a refactoring
(b6c3cb0)

The duration is based on the number of continuous errors, but maximized in one minute

related issues: #508 #509

Dockerfile enhancements

Dockerfile : bug fixes. 
Perhaps "COPY requirements.txt ./requirements.txt" is unnecessary but it doesn't hurt (instead of "COPY requirements.txt .")

Simpson screenshot search engine

[fix] typo

[enh] WolframAlpha no API engine (and tests for both)

 - searx/settings.yml is the right name in second sed line
 - COPY requirements.txt . does not work: "Not a directory"

Conflicts:
	searx/tests/test_engines.py