Make Python 3 able to read settings files with Unicode characters

SearX currently doesn't start up when run with Python 3 as it tries to parse the
settings.yml file with ASCII codecs.
There are similar problems with engines_languages.json and currencies.json
Python 3 requires that files with Unicode characters be read with a 'b' flag.
This also works with Python 2 and hence can be integrated into the main source
code.

Tested with the latest Python 3.6.4rc1 on Debian unstable.

Signed-off-by: Joseph Nuthalapati <njoseph@thoughtworks.com>