Adds BootstrapValidator behavior

I have added [BootstrapValidator](https://github.com/nghuuphuoc/bootstrapvalidator) to the behaviors.

The [options/settings](http://bootstrapvalidator.com/settings/) can be passed into the behaviors options

```js

  behaviors: {
    bootstrapValidator: {
      message: 'The field is not valid',
      feedbackIcons: {
        valid: 'fa fa-check',
        invalid: 'fa fa-times',
        validating: 'fa fa-refresh'
      }
    }
  }

```

The form target could be done better, do you have any suggestions/comments?

For now, it expects the target form to be declare into `this.view.ui.form`.

``` js
  ui: {
    form: 'form#myform'
  }

```

Also, I am not sure if (and how) events binding behaviors (like `success.form.bv` or `error.field.bv`) should be handle within this library or into the dev's app directly.

:v: 
use `_.isString(target)`