Add drag and drop and tool tip demo pages, fix bugs

[cmeyer]

• Add drag and drop to a list view, with a drop landing between items.
• Fix a canvas window leaving its widgets and canvas items open when it closes.
• Demonstrate item tool tips in a list box and a list view in the ui demo.
• Fix an image taking the mouse when a click on it does nothing.
• Add methods to a list view for an image of an item and where it is drawn.
• Demonstrate drag and drop between two list views in the ui demo.