Add support for $after and $tab to $form->addHeader()

[Makoto]

Simple suggestion to make third-party stuff a bit more neat. I may want to add a header to separate my content when inserting form elements like so,

	/**
	 * Add Input
	 *
	 * @param	\IPS\Helpers\Form\FormAbstract	$input	Form element to add
	 * @param	string|NULL					    $after	The key of element to insert after
	 * @param	string|NULL					    $tab	The tab to insert onto
	 * @return	void
	 */
	public function add( $input, $after=NULL, $tab=NULL )

But addHeader does not support $after and $tab as arguments at the moment,

	/**
	 * Add Header
	 *
	 * @param	string	$lang		Language key
	 * @return	void
	 */
	public function addHeader( $lang )

Very minor, but would be an appreciated addition!

[bfarber]

I've raised the request internally for consideration.

[Makoto]

Wonderful, thank you @bfarber.