new preferences handling

Preferences class was introduced in order to handle user preferences. Right now
it parses cookies and the form in preferences. Also it can retrieve settings
based on the name of the setting.

ATTENTION
Please note that engine preferences are handled differently from now on. So it
introduces incompatible changes. Every user who has saved preferences should reset and
save his/her settings again.

This change was needed, because everytime a default disabled engine was
added saved user preferences would broke. Now engine setting tracking is
fixed.

searx/search.py

@@ -23,7 +23,7 @@ from searx.engines import (
     categories, engines
 )
 from searx.languages import language_codes
-from searx.utils import gen_useragent, get_blocked_engines
+from searx.utils import gen_useragent
 from searx.query import Query
 from searx.results import ResultContainer
 from searx import logger
@@ -140,15 +140,13 @@ class Search(object):
         self.lang = 'all'
 
         # set blocked engines
-        self.blocked_engines = get_blocked_engines(engines, request.cookies)
+        self.blocked_engines = request.preferences.engines.get_disabled()
 
         self.result_container = ResultContainer()
         self.request_data = {}
 
         # set specific language if set
-        if request.cookies.get('language')\
-           and request.cookies['language'] in (x[0] for x in language_codes):
-            self.lang = request.cookies['language']
+        self.lang = request.preferences.get_value('language')
 
         # set request method
         if request.method == 'POST':
@@ -294,11 +292,8 @@ class Search(object):
             else:
                 request_params['language'] = self.lang
 
-            try:
-                # 0 = None, 1 = Moderate, 2 = Strict
-                request_params['safesearch'] = int(request.cookies.get('safesearch'))
-            except Exception:
-                request_params['safesearch'] = settings['search']['safe_search']
+            # 0 = None, 1 = Moderate, 2 = Strict
+            request_params['safesearch'] = request.preferences.get_value('safesearch')
 
             # update request parameters dependent on
             # search-engine (contained in engines folder)