C1TreeView CheckBoxes
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Shows how to add checkboxes to nodes in a C1TreeView control.

Each node in a C1TreeView has a Header element which may contain any UIElement. The 
sample defines an ItemHeader class that contains a CheckBox control and a TextBlock.
It then assigns ItemHeader objects to the node's Header property.

You can customize the C1TreeView by creating custom headers designed to contain any 
information and/or visual elements your application needs.

The default header for the C1TreeViewItems is of type String. The C1TreeView supports 
auto-search and find operations for the default header.

Due to the String comparison used by this functionality, when using a custom header
that is not of type String, you should provide a TypeConverter to indicate the tree how
to convert any header to a String representation, so it can be used in auto search and 
find operations.

This sample includes an implementation of a TypeConverter (CustomItemConverter class)
that contains the logic to convert the custom headers to its string representation.

