Repair defunct World Wind Java examples

[pdavidc]

The following World Wind Java examples no longer function correctly, throw exceptions, or appear to be obsolete. Evaluate these examples for relevance and remove or repair as necessary:

• DynamicLayerDisplay
• ExtrudedPolygonsFromShapefile
• PersistSessionState
• ScreenSelection
• SplitPaneUsage
• WebBrowserBalloons

[pdavidc]

Removed the obsolete DynamicLayerDisplay example. This capability is built in to the layer manager used by all examples.

[pdavidc]

Updated and simplified the ExtrudedPolygonsFromShapefile example. Rather than requiring the user to find and load a shapefile containing extruded polygons, this example now loads one automatically.

[pdavidc]

Repaired a bug causing PersistSessionState to throw exceptions on startup.

[pdavidc]

Repaired a bug causing SplitPaneUsage to throw exceptions when the WorldWindow is made to disappear.