#12 Option to log failed searches

failData = {
  "{INSTANCE_URL}" : {
    "{REASON_CODE}": [
      (datetime, extra_msg),
      (datetime, extra_msg),
      ..
    ]
  }
}

Ability to log failed searches, this should be optional. It will make it easier to notice failing instances so they can by put on the blacklist, or on a timeout but that hasn't been implemented yet. #### Notes: Use `class ErrorType` (searxqt/core/requests.py) as the error type. Fields to log: - datetime - instance url - error type - extra msg Possible struct: ``` failData = { "{INSTANCE_URL}" : { "{REASON_CODE}": [ (datetime, extra_msg), (datetime, extra_msg), .. ] } } ```