Google Site Verification key support

Enables Grunt deployment to push a google-site-verification file based
on a value in keys.json.
Shorten up the debug output section

This will add some additional vertical room for the expanded caching
section.
Shorten up existing cache button labels

Reduces both the summary and result labels.
Expose new methods on router

Allows other modules to get the failure count and to clear it.
Add support for clearing failures

This is done via the advanced tab of the configuration screen.
Documentation update

Updates the screenshot for Forget Failures and explains its
functionality on the advanced configuration page.
Merge branch 'add/forget-failures' into develop

Adds support for the user to tell AwesomeTTS to forget cached failures.