[Button] implement [buttontype, labelSide]

[grzegorzdec]

also fix docs

<linearLayout localPosition={[0, 0.75, 0]}>
	<button text='text' height={0.15}/>
	<button iconType='clock' text='text' height={0.15}/>
	{/* labelSide has no effect for text-with-icon button type */}
	{/* the 'icon-with-text' type is not supported */}
	<button type='text-with-icon' labelSide='right' iconType='clock' text='text' height={0.15}/>
	<button type='icon-with-label' labelSide='top' iconType='clock' text='text' height={0.15}/>
	<button type='icon-with-label' labelSide='right' iconType='clock' text='text' height={0.15}/>
	<button type='icon-with-label' labelSide='bottom' iconType='clock' text='text' height={0.15}/>
	<button type='icon-with-label' labelSide='left' iconType='clock' text='text' height={0.15}/>
	<button type='icon' labelSide='left' iconType='clock' text='text' height={0.15}/>
	<button type='text' labelSide='left' iconType='clock' text='text' height={0.15}/>
</linearLayout>