Extract SVG width and height

[le717]

src/SvgSize.js

• Fully extract width, height, viewBox and enable-background attribute values every time they are present
• Extract values from AI, Inkscape, and minified (svgo tool) SVGs
• Handle case if one, both, or all attributes are missing

main.js

• Special routine for handing SVG graphics only
• Update input fields once the width/height is extracted
• Blank the inputs if no size is detected after one is

CSS

• Do not disproportionately display SVGs

[le717]

Completed by #25.