macOS Signing Scripts: Add module responsible for notarization.

The new notarize module submits, waits for results, and staples tickets
from Apple's notary service. The module is wired into the pipeline
module that orchestrates all the operations, but the driver script
sign_chrome.py currently defaults to not notarizing. Notarization will
be made default at a later time.

This CL also introduces a new notarize_app.py wrapper script for
submitting and waiting for notarization on arbitrary artifacts.

Bug: 850199
Change-Id: I25af5beb4f8e19247f28a3122e38fb6a67c2e847
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1663168
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672293}
14 files changed