[fix] read utf-8 files (settings, languages, currency) with python3.5

Related to discussion in #1124
The io.open import is necessary for python2

searx/__init__.py

 import logging
 from os import environ
 from os.path import realpath, dirname, join, abspath, isfile
+from io import open
 from ssl import OPENSSL_VERSION_INFO, OPENSSL_VERSION
 try:
     from yaml import load
     raise Exception('settings.yml not found')
 
 # load settings
-with open(settings_path, 'rb') as settings_yaml:
+with open(settings_path, 'r', encoding='utf-8') as settings_yaml:
     settings = load(settings_yaml)
 
 '''

searx/engines/__init__.py

 import sys
 import threading
 from os.path import realpath, dirname
+from io import open
 from flask_babel import gettext
 from operator import itemgetter
 from json import loads
 
 categories = {'general': []}
 
-languages = loads(open(engine_dir + '/../data/engines_languages.json', 'rb').read())
+languages = loads(open(engine_dir + '/../data/engines_languages.json', 'r', encoding='utf-8').read())
 
 engine_shortcuts = {}
 engine_default_args = {'paging': False,

searx/engines/currency_convert.py

 import sys
 import unicodedata
 
+from io import open
 from datetime import datetime
 
 if sys.version_info[0] == 3:
     global db
 
     current_dir = os.path.dirname(os.path.realpath(__file__))
-    json_data = open(current_dir + "/../data/currencies.json", 'rb').read()
+    json_data = open(current_dir + "/../data/currencies.json", 'r', encoding='utf-8').read()
 
     db = json.loads(json_data)