TinyMCE help modal:
- Don't load the old tiny_mce_popup.js.
- Add the shortcut for <code> and the second shortcut for link to the shortcuts listing.
- Update some of the text.
See #27100

git-svn-id: https://develop.svn.wordpress.org/trunk@28027 602fd350-edb4-49c9-b593-d223f7449a82