Convert the main flow of skiaperf into a Polymer app.

For now we just copy over all the core- and paper- elements into
"res/imp/". In the future we may swich to vulcanize to pre-process
the imports.

BUG=skia:

Review URL: https://codereview.chromium.org/673853002
Revert of perf/go/flags -> perf/go/init (patchset #4 id:60001 of https://codereview.chromium.org/678453002/)

Reason for revert:
Prevents flags from being processed.

Original issue's description:
> perf/go/flags -> perf/go/init
>
> BUG=skia:
>
> Committed: https://skia.googlesource.com/buildbot/+/646df87c5944269b92cb36e30b7a2a99371e9c63

TBR=mtklein@google.com,tfarina@chromium.org,mtklein@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/675633004
Fix relative directories in scaffold-sk definition.

BUG=skia:
TBR=borenet

Review URL: https://codereview.chromium.org/673883003