Move the logic of the antibot to a service

Thanks @hmendes, can you review it again, please?

It guess we could change this part

    $skip_antibot = FALSE;

    // Set skip antibot to true if user has appropriate permission.
    if ($this->user->hasPermission('skip antibot')) {
      $skip_antibot = TRUE;
    }

to

   $skip_antibot = $this->user->hasPermission('skip antibot');

But its not a required change, so I'll change to RTBC anyway.

Patch for 2.0.x

I have done one round of reroll and pushed in a minor improvement as well from the suggestion in #6. Let's avoid the patches and use the merge request workflow for further development. Also, some test changes would also be good for this change.

I'd like to work on this but It seems like there are some conflicts to resolve before.