Update icons to match new style

[miguelsolorio]

See microsoft/vscode#8017 (comment), this updates all of the icons to match the new style. Also tried fixing some alignment/spacing issues with the new sizes:

[RMacfarlane]

Thanks @misolori! There’s only one icon that looks a bit weird to me, the diff.svg that’s shown when a reviewer has requested changes:

Is there anything that looks more like the original? Now that I know the filename is diff it makes sense to me, but when I first saw it in this context I was confused about what it was. Maybe it would be better to remove that icon from the extension and just use the ‘x’ instead?

Do we have a version of https://octicons.github.com/icon/request-changes/?

[miguelsolorio]

@RMacfarlane thanks, let me see if I can find an alternative that matches that or create a similar one.

[miguelsolorio]

I've update the requested changes icon to match https://octicons.github.com/icon/request-changes/

[RMacfarlane]

Thanks!