RevitSdkSamples/snapshot/2008/SDK/Samples/LevelsProperty/CS

This sample should provide the following functionality:

1. When the command is executed, a dialog should appear and display all Levels in the existing document, with their name and elevation.

2. You may modify every Level's name and elevation

3. You may use the 'Add' button to add a Level, and also use the 'Delete' button to delete a Level.

4. When you click the 'OK' button, all changes should be applied to the model. 

5. When you click the 'Cancel' button, all operations shouldn't be validated.