Edited Feature: PropertyGrid Expand/Collapse All Properties [22227]

Based on discussion https://wpftoolkit.codeplex.com/discussions/653192.

User wants to be able to collapse/Expand properties with methods.
Comments: ** Comment from web user: BoucherS **

This will be fixed in v3.1.
The following methods will be available in the PropertyGrid :
-CollapseAllProperties()
-ExpandAllProperties()
-ExpandProperty( string propertyName )
-CollapseProperty( string propertyName )