[Runtime][Tizen] Support to set app window view mode by configure config.xml.

We support configuring application window display mode by 'display'
field in manifest.json for XPK packages. While this way is not enabled for widget format
packages.

The Widget Spec tells that 'viewmodes' attribute denotes the author's
preferred view mode.
http://www.w3.org/TR/2012/REC-widgets-20121127/#the-viewmodes-attribute

This CL enables the 'viewmodes' attribute for Widget applications.

BUG=XWALK-1732