New features:
* Gather mode launches the browser, collects artifacts, saves them to disk, and quits.
* Audit mode skips browser interaction, loads artifacts from disk, runs audits on them, generates report
* --gather-mode and --audit-mode are the long versions of -G and -A.
* -GA is also supported. Normal run, but saves artifacts to disk for subsequent -A runs.
Other changes:
* config.auditResults is removed
* assetSaver got a new impl of saveArtifacts, and added loadArtifacts
* --save-artifacts CLI flag was removed
Chris Thompson
Rupesh
Paul Irish
Brendan Kenny