Update demo page

* Change urls to the CDN version of files
* Update link and css refs to latest versions
* Add additional help text (keyboard shortcuts, etc)
* Add separate links back to repo and to dev docs
Add zing
Re-arrange Sharing Selection to be clearer; spelling
Don't use local script for knockout or editableCell; standarize CDN
Merge pull request #28 from gnab/readme-with-zing

Readme with zing