new Cascading Choice Parameter type

This new parameter type will allow a jenkins user to create a dynamic choice parameter whose options are based on the value of another parameter. The configuration is very similar to the Dynamic Choice Parameter with the addition of a "Parent Property Name" property which allows the user to specify which property the Cascading Property depends on.


In the example below, you can see that I am configuring a choice parameter named parentProp1 and a cascading choice parameter named childProp1 that depends on the value of parentProp1 to create it's options.

![image](https://f.cloud.github.com/assets/1045684/775240/8d053f3e-e96d-11e2-8b18-87f62a14c382.png)

And here is what this looks like when you click build:

![image](https://f.cloud.github.com/assets/1045684/775262/f38ff2bc-e96d-11e2-8e5f-34766770f920.png)