SkQP: better error report workflow

  * Generate report in app after running all tests.
  * Add script to unpack backup.ab file.
  * Remove unused index file.
  * Streamline instructions in README.md.

Change-Id: I44c80b17332eb4496ee31578287b691bd646d71a
Reviewed-on: https://skia-review.googlesource.com/86742
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Hal Canary <halcanary@google.com>
9 files changed