Throw error with meaningful message if changeset is invalid

[jelhan]

Ember Bootstrap Changeset Validations throws an error without an error message if the model is invalid:

ember-bootstrap-changeset-validations/addon/components/bs-form.js

Lines 20 to 22 in 3ccdf4c

	if (!model.get('isValid')) {
	throw new Error();
	}

To ease debugging, the error should have a meaningful message.