Warn users about potential overwritten files

The current wizard has the potential for overwriting project files silently, which isn't a good precedent. We currently prompt the user for the path to the generated camel file but don't allow them to specify the file name. And any generated Java files in the Java location have the potential for being overwritten as well.

For Java files, we can put a warning in the wizard page suggesting that things will get overwritten.

For the Camel config, I propose that we add the file name to the path and more explicitly test to see if that file exists ahead of time, warning the user that it will be overwritten.

The problem with warnings is they don't prevent the wizard from enabling "Finish" on the first page of the wizard, so they may not see them.