Added input type="submit" support

See #171
Would be cool if we could make this check a little more advanced since the primary etc style types are only necessary when the type is button and the button has its own checks for this anyway, we could just disable the check for that type, something like this:
```
bsStyle: function(props) {
	if (props.type === 'submit') {
		// Return early if `type=submit` as the `Button` component
		// it transfers these props to has its own propType checks.
		return;
	}

	return React.PropTypes.oneOf(['success', 'warning', 'error']).apply(null, arguments);
},
```