Extend widget instance only with chosen definition's properties

[Piotrek Koszuliński]

Currently we load all definition's properties to widget instance. We should only load init method and perhaps nothing more.

In some places code tries to access widget.dialog property and so on, but this should be changed to widget.definition.dialog.

Also, widget.repository and widget.definition should not come from definition object, but should be set in widget's constructor.