Added missing SVG attributes

[jonase]

Added fill-opacity, font-family, font-size, opacity, stroke-opacity attributes. Fixes #1171.

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[zpao]

Do all of these style attributes really add a lot? I ask this because we moved away from these things in HTML years ago and stuck them in style. font-family is pretty crazy being an element, an attribute, and on style. I don't work with SVG so I'm in the dark here.

[jonase]

Which attributes should be present? For example fill and stroke are currently supported by React but not fill-opacity and stroke-opacity. I think the easiest way to decide is to simply follow the SVG spec. Any other approach seems arbitrary.

[pedroteixeira]

Hi, I see lots of PR and issues about SVG. Is there any expected version date for having these missing SVG tags/attributes support in React?

[syranide]

@pedroteixeira #1657

[zpao]

We shouldn't need this one since the case & spelling is identical.

[zpao]

FYI, I removed this line when I merged it in.

[zpao]

Thanks!