Add accidentally removed import to search.py

[kvch]

When reverting "remove 'all' option from search languages" (#1475) was merged, an import got removed accidentally. This leads to the following error in the console:

Exception in thread 419709b5-6c9a-472f-9337-55b5520e4c7a:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
    self.run()
  File "/usr/lib/python2.7/threading.py", line 754, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/home/n/p/searx/searx/search.py", line 150, in search_one_request_safe
    engine.suspend_end_time = time() + min(settings['search']['max_ban_time_on_fail'],
NameError: global name 'settings' is not defined

This PR adds the import again.
@Pofilo if you have time, please review the PR.

[Pofilo]

Perfect !