Add Grunt task for enabling debugging of subsequent tasks.

This is accomplished by spawning a child instance of Grunt with the
`--debug` or `--debug-brk` options of node set, to allow debugging.
Fix test script URLs, add favicons to test pages.
Upgrade Siesta to version 2.0.3.
Re-enable Siesta tests after SauceLabs update.
Modify default Grunt domain to match webserver default.