Modernize the main Chrome API Javascript files and make into a plugin

Includes splitting chrome.Event into its own module.
Move Chrome API JS files into api/ subdirectory
Moving the integration files around.
More refactoring of core plugin

- Move README to the top level and update it.
- Move iosbuildstep to the top level since it's not really part of www.
- Add <asset> tags to plugin.xml
Update our grunt setup and README

Now using grunt 0.4, and the README reflects the current plugin
structure.
Merge branch 'plugins' of github.com:MobileChromeApps/chrome-cordova into plugins