[Runtime] Add manifest handler for widget packaged applications.

The CL parses manifest keys required by JavaScript widget interface,
and save mapped key value pairs in ManifestData, so that it can be read
by widget extension.

We can also extend this CL to validate the widget configuration keys in
future.
[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.