Created a dialog to confirm things, like for now the "shred" of a file. Made it so that other dialogs can be created with it.
Created the confirm dialog for the shredder. However, I made it so that the dialog could be user for more than just a confirmation. You can give a list of desired input types and the dialog will construct the list with corresponding input fields. This way we could create the mass renamer, see #85
Now the selection stays if pressed action was not performed successfully.
did some refactoring and added javadoc. Also added the possibility to reverse the colors on the dialog buttons and to even disable one or the other. This gives the possibility to create a dialog with just 1 button, like "ok".
Merge pull request #140 from AlexKolpa/139-confirm-dialog

Confirm dialog for shredder

closes #139