pep8 is deprecated, it is replaced by pycodestyle.

Move spot project to python 3. The support of python 2 is
removed related to the issue https://github.com/asciimoo/searx/issues/1471.

The update is mainly done with `2to3` tool and a lot of changes for
the unicode support (see https://docs.python.org/3/howto/unicode.html)

Close: #7

Engines was stored in set and casted in list, it leads to
issue during merge of result. This patch fixes the engines
container to a list to be able to use json serialization.

Below the error spotted:
```
   File "/usr/local/searx/searx/results.py", line 233, in _merge_result
     duplicated['engines'].add(result['engine'])
 AttributeError: 'list' object has no attribute 'add'
```

Previously, if a same result was returned from the
same engine, the name of the engine would be added
more than once. To eliminate engine name duplication
engine list was changed to set.

Purposes :
- isolate the plugins calls
- distinction between parsing the web request and running the search (Search class). To be able to test code easily, to run searx code outside a web server, to filter the search query parameters with plugins more easily, etc...

Details :
- request.request_data contains request.form or request.args (initialize inside pre_request() function)
- Query class is renamed RawTextQuery
- SearchQuery class defines all search parameters
- get_search_query_from_webapp create a SearchQuery instance (basically the previous Search.__init__ code)
- Search class and SearchWithPlugins class takes a SearchQuery instance as class constructor parameter
- SearchWithPlugins class inherites from Search class, and run plugins
- A dedicated function search_with_plugins executes plugins to have a well define locals() (which is used by the plugins code).
- All plugins code is executed inside the try...except block (webapp.py, index function)
- advanced_search HTTP parameter value stays in webapp.py (it is only part of UI)
- multiple calls to result_container.get_ordered_results() doesn't compute the order multiple time (note : this method was call only once before)
- paging value is stored in the result_container class (compute in the extend method)
- test about engine.suspend_end_time is done during search method call (instead of __init__)
- check that the format parameter value is one of these : html, rss, json, rss (before the html value was assumed but some text formatting wasn't not done)

also minor changes in attributes and images from wikidata

TODO:
    merge attributes

[mod][fix] use the average of results number ++ do not display smaller result number than the actual result count - closes #600

creates simple multilingual infobox using wikipedia's api

Related to #428, which was fixed in e3df22b1 but broken in a refactoring
(b6c3cb0b)

Several changes has been made:
 - Parallel result merge
 - Scoring algorithm slightly changed (see result_score())
 - Proper Thread locking on global data manipulation