Allow inline svg handling Variable elements in skins

I needed the skin parser to be able to manage Variable elements in svg for cues and loops buttons so I added a function to do it and hooked it directly if a svg element is present in a (un)pressed element.

So now, I can handle inlined svg in my pushbuttons like this : 
```xml
<Pressed>
	<svg height="16" width="16">
		<rect x="0" y="0" width="16" height="16" style="fill:#000000; stroke-width:1; stroke:#ff0000; stroke-linecap:sqare;" />
		<text x="0" y="15" style="fill:#ff0000; font-size: 16px; font-weight: bold;">
			<Variable name="number"/>
		</text>
	</svg>
</Pressed>
```

Should I continue in this direction and do I do this well?
If yes, what do you think I should begin with?

Thanks in advance!