Fix symbol render

Fixed a bug that was not transferring the transform attribute from use tag to cloned tag.
Added attribute "instanced_by_use" to tags cloned to divide symbols from used symbols.
Added symbol to the list of tags not to be rendered ( if not instanced )
Changeg viewbox transform function to take care of all the tags that can support viewbox attribute.
For tags that are not svg, scale factor is ignored till we can sort out how to use 100% value for width attribute
is not really referenced, is more a instance of the object really. is
copied as many times as you need to reference it.
if you prefer more suitable name of course is ok, but for this situation is
better "instanced by" than " referenced in" we need it to distinguish
between the symbol we should render and the one not.

In src/parser.js:

> @@ -439,6 +439,7 @@
>        }
>
>        el2.setAttribute('transform', currentTrans);
> +      el2.setAttribute('instanced_by_use', '1');

Not sure this is a good wording. Do you mean "referenced in use tag"?

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