[Tizen][Runtime] Implement Widget API.

This commit supports Widget API on Tizen(exclude 'preferences' attribute).
The API provides application programming interfaces that enables ability
to access some of the metadata declared in a widget's configuration
document, such as 'name', 'author', 'description'.

Spec:
http://www.w3.org/TR/widgets-apis/#the-widget-interface

The 'preferences' attribute implementation will be provided later.