Custom properties for fill and stroke colors

[rafaeltavares]

It will be awesome if we could change the svg stroke colors too.

[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project, in which case you'll need to sign a Contributor License Agreement (CLA).

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Once you've signed, please reply here (e.g. I signed it!) and we'll verify. Thanks.

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[rafaeltavares]

I signed it!

[googlebot]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for the commit author(s). If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.

[rafaeltavares]

I added the other email to my account.

[googlebot]

CLAs look good, thanks!

[notwaldorf]

i think it would be best if both of these were custom properties --iron-icon-fill-color and --iron-icon-stroke-color, for example, which would have the default values as currentcolor. That was somebody could customize them after the fact. What do you think?

[rafaeltavares]

Seems to be the perfect match.
I already committed the changes.

[notwaldorf]

Would you mind squashing your commits into 1, and then I can merge this? Thanks so much!

[rafaeltavares]

Everything set.
Thanks!

[notwaldorf]

Thanks!