Support Style Attribute

Carve should support the style attribute which is used extensively in Inkscape and other programs so that Carve can properly display and roundtrip files. Thus, we should parse the style attribute and override those values on that element. Note that the 'style' attribute is not part of SVGT 1.2, but it is part of SVGF 1.1.

For instance:

<rect fill="red" style="fill:green" /> should produce a green rectangle in Design mode.

NOTE: Should definitely add the 'style' attribute to the Properties pane for all visible element types so that the user can edit both style/fill values simultaneously.