Add -webkit to all keyframe definitions without -webkit

:warning:  This fixes a quite critical bug.

I've heard of spinners not animating for some in Chrome. They've been working fine for me, and it doesn't seem to be dependent on your setup/Chrome version. I haven't been able to figure out why this is happening, but I've figured out how to fix it.

The problem seems to be that Chrome supports `@keyframes` definitions without the `-webkit` prefix. Chrome doesn't, however, support `transform` without the `-webkit-` prefix. So even though `@-webkit-keyframes` is defined, `@keyframes` takes precedence, and nothing animates. This PR adds `-webkit-` to all transformations inside all `@keyframes` blocks.

(What makes no sense is that if this really is the case, it should never have worked in Chrome.)