Integrate Unity Web API with Midori's app mode

Ubuntu 12.10 has a new plugin for Firefox and Chrome called Unity Web Apps, which integrate webapps with the Messaging Menu, Sound Menu, Notify OSD, etc. There's a similar project called Fogger, but this one is also starting to develop support for Unity Web API.

Midori should implement support for Unity Web API in the following way:
* When navigating a supported website, show the prompt “Would you like to integrate {webapp} with the desktop?”
* If the user agrees, create a new app (like Fogger does).
  Don't just start integrating the webapp inside a normal browser instance, since this is very confusing.
* Launch the newly created app immediately.
* If the user wants to launch the app later, it will be found in the application launcher (Slingshot, Unity Dash, etc).

Midori should also include a webapp manager to add or remove webapps.