[fix] duckduckgo's xpaths changed

for some reason installing grunt globally caused travis test to fail.

test_duckduckgo modified to reflect changes in duckduckgo's html

Update link to documentation page

[fix] improve argument parsing of manage.sh

Translation fix

add new languages:
* bg
* el_GR
* eo
* pt_BR

[enh] autocompletion : add qwant

WolframAlpha infobox

setting async to false in the request did the job, lol.

changes were made for wolframalpha infobox:

    - wrap text inside infobox.
      for example, there's a hill in New Zealand called
      Taumatawhakatangihangakoauauotamateapokaiwhenuakitanatahu
      (don't blame me, blame the Kiwis)
      and now it doesn't break the infobox.

    - add an optional image field for infobox's attributes.
      (doesn't affect ddg infobox at all)

    - table is now always split in half.
      needed so that images stay inside infobox.
      (max-width doesn't work for inline elements, it's the table
      that has to set the width.

if you don't like how the table width looks now in ddg/wiki's infobox,
i can change that code so that the style only applies when using
wolframalpha.

TODO:
    - infobox styles
    - unit tests

ISSUES:
    - no_api version needs to re-call server for additional pods, such
      as plots. therefore, it's even slower than before. comment out the
part that calls get_async_pod if requests reach timeout or increase
timeout in settings.yml.

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