[IZPACK-1069] Allow dynamic views on panels

This is to address http://jira.codehaus.org/browse/IZPACK-1069
Refer to the link above for more information.

Allows a checkbox or radio button to show additional fields on the same userInputPanel, if conditions specified correctly. Ensures that fields are not validating during this process, validation only needs to occur when pressing the next button.

Allow specifying the topBuffer as number of pixels with the "rigid" attribute. This comes naturally and dynamically showing and hiding fields make the spacing between the top field and title change.

Let me know if anything needs clarification, and am fully open to feedback!

~~EDIT: Forgot to add functionality in console mode. Currently work in progress.~~
Checks to see if a console field should be displayed have been added, but I realize it kind of duplicates the code from the updateView() method of the GUI type fields. I plan to eventually come back to this in a seperate PR and find a way to abstract this out.