Flake8 and Twitter corrections

Lots of Flake8 corrections
Maybe we should change the rule to allow lines of 120 chars. It seems more usable.

Big twitter correction : now it outputs the words in right order...

searx/engines/500px.py

@@ -35,9 +35,9 @@ def request(query, params):
 # get response from search-request
 def response(resp):
     results = []
-    
+
     dom = html.fromstring(resp.text)
-    
+
     # parse results
     for result in dom.xpath('//div[@class="photo"]'):
         link = result.xpath('.//a')[0]