Created PropertyValueModel and changed the property value listing to use that model.

PropertyValueModel will be used to implement the editing using the editing interface of Qt models after our own model supports it.
Prototype editing support to PropertyValueModel. Also removed propertyValue and vault properties from DataType specific controls as they are already visible through TypedValue control.
Added property value normalization when fetching property values.
 - Strip Favorite view and Accessed by me property values from the "Property values for display" set.
 - Ensure HasValue field is specified for TypedValue
 - Ensure empty single-line text always has the value field set to empty string. Previously the whole field was missing.