[Tizen][Runtime] Enable hosted app support on Tizen.

On Tizen, a web application use ```<tizen:content>``` to set entry page will be recognized as hosted app, and will cover the element ```<content>``` without  tizen namespace.This patch will enable this feature in Crosswalk
runtime.

BUG=XWALK-1492
Oh, well this is not a bug :) it comes from 712085e811be6343ce4da061d866ac8070503089 which is "[Runtime] Fix launch issue for widget applications that don't have   'content' element in config.xml." .
If your patch is merged as it is this problem will immediately turn up again :)

I'd recommend just to move the code which is handling the "widget applications without config.xml"  from Application::GetAbsoluteURLFromKey (this code is right after "FIXME: Refactor this Widget specific code out." comment) to Application::GetStartURL. 

Pls. ping me on IRC if you have any questions reg this.