#26321: [Desktop] Unable to click on the back button to change config path

*Story*
As a Toolkit user setting up a project, I want to be able to click on the back button to change the configuration folder path is I enter an invalid value.

*Description*
When setting up a project, if you set the config and the storage location with the same path you will get an error saying that you can't do that. (See the attached file)
When getting this error, the only option you have is to cancel the set up.

The general idea would be to add a pre-setup validation method to the wizard and then update the GUI so that right before it goes to the setup page it calls it and if there is a failure it should go to a page that reports on the error and makes you go back and fix it rather than the setup.

Hey there, this was my suggestion to try and make the wizard act properly if new pages are added or the page order changes.  The idea was that whatever page is the last page is the one that should call the pre_setup_validation, and that logic applied to all setup project pages, thus belonged in the base class.

A comment to that effect would definitely be good (also a good reason why somebody involved in the design might not be the best code reviewer).