Use custom view for TSMessage (model and view)

Now we can subclass and create own controls under TSMessageView.
I have also separate view and model (item). 
Please check example TSMessageCustomItem and TSMessageCustomView.

```Objective-C
TSMessageCustomItem *item = [TSMessageCustomItem itemWithTitle:@"Test" subtitle:@"description" type:TSMessageNotificationTypeSuccess inViewController:self tapHandler:^(TSMessageCustomItem *item) {
        NSLog(@"Message did pressed");
    } iconHandler:^(TSMessageCustomItem *item) {
        NSLog(@"Icon did pressed");
    } disclosureView:nil disclosureHandler:^(TSMessageCustomItem *item) {
        NSLog(@"Disclosure view did pressed");
    }];
[TSMessage showNotificationMessageWithItem:item];
```