Switch to non-stock Sisyphus for better integration with Gravity Forms

This PR covers a number of issues:

- Update to current Sisyphus 6aa8ecc
- Support for paged forms ee806788f197d85cae25482b77644ebb24c8e5a7
- Multi-part date field restored all three fields with contents of the third 22d242a41d724a272e873e0d2590503c7ac9b52e
- Sisyphus altering Gravity's hidden fields 429bb0d2614d8a5f02d9052994b7e625eee5b4a9
- Sisyphus creating excessive entries during Chrome autocomplete 22d242a41d724a272e873e0d2590503c7ac9b52e

Naturally this involved a few edits to Sisyphus and therefore I also included a Gruntfile for minifying the pretty version. The plugin as I'm submitting here won't work, of course, until a minified file has been generated with the default grunt task. Is that the way to do this or should I just include a minified copy as well?

This is my first pull request so let me know if you want these commits squashed or split up or whatever...
Happy to accommodate :)