[mod] Dailymotion: improved request API & upgrade to data_type: traits_v1

- fetch_traits(): fetch locales (and languages) from dailymotion API
- removed obsolete data-type "supported_languages"
- add documentation
- improved argument list of the HTTP request:
  - add argument: family_filter_map
  - add conditional argument: localization
    Don't add localization and country arguments if the user does select a
    language (:de, :en, ..)
- improve code quality (mainly improve readability)

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

docs/src/searx.engine.dailymotion.rst

@@ -0,0 +1,8 @@
+.. _dailymotion engine:
+
+===========
+Dailymotion
+===========
+
+.. automodule:: searx.engines.dailymotion
+  :members: