[enh] google engine: supports "default language"

Same behaviour behaviour than Whoogle [1].  Only the google engine with the
"Default language" choice "(all)"" is changed by this patch.

When searching for a locate place, the result are in the expect language,
without missing results [2]:

  > When a language is not specified, the language interpretation is left up to
  > Google to decide how the search results should be delivered.

The query parameters are copied from Whoogle.  With the ``all`` language:

- add parameter ``source=lnt``
- don't use parameter ``lr``
- don't add a ``Accept-Language`` HTTP header.

The new signature of function ``get_lang_info()`` is:

    lang_info = get_lang_info(params, lang_list, custom_aliases, supported_any_language)

Argument ``supported_any_language`` is True for google.py and False for the other
google engines.  With this patch the function now returns:

- query parameters: ``lang_info['params']``
- HTTP headers: ``lang_info['headers']``
- and as before this patch:
  - ``lang_info['subdomain']``
  - ``lang_info['country']``
  - ``lang_info['language']``

[1] https://github.com/benbusby/whoogle-search
[2] https://github.com/benbusby/whoogle-search/releases/tag/v0.5.4

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