Extended MZFormSheetSegue functionality to configure MZFormSheetController before presentation and presentation completion handler.

Now this code is possible:
```
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if ([segue.identifier isEqualToString:@"segue_result"])
    {
        ABResultViewController *resultController = segue.destinationViewController;
        // ...
        // Configuring MyResultViewController
        // …
        
        MZFormSheetSegue *formSegue = (id)segue;
        formSegue.formConfigHandler = ^(MZFormSheetController *formSheetController)
        {
            formSheetController.shouldDismissOnBackgroundViewTap = YES;
            formSheetController.transitionStyle = MZFormSheetTransitionStyleBounce;
            formSheetController.cornerRadius = 8.0;
            formSheetController.portraitTopInset = (self.view.bounds.size.height - 325)/2 + self.sharePanel.bounds.size.height/2;
            formSheetController.presentedFormSheetSize = CGSizeMake(270,325);
            formSheetController.shadowOpacity = 0.0;
            [formSheetController setDidTapOnBackgroundViewCompletionHandler:^(CGPoint location) {
                //[this performSegueWithIdentifier:@"segue_back" sender:nil];
                [self animatedHideSharePanel];
            }];
        };
        formSegue.completionHandler = ^(MZFormSheetController *formSheetController){
            [formSheetController.view addSubview:self.sharePanel];
            self.sharePanel.hidden = NO;
            self.sharePanel.center = CGPointMake(self.view.bounds.size.width/2, -self.sharePanel.bounds.size.height/2);
            [UIView animateWithDuration:0.2 animations:^{
                self.sharePanel.center = CGPointMake(self.view.bounds.size.width/2, self.sharePanel.bounds.size.height/2);
            }];
        };
    }
}
```