Specific ctkFileDialog::setBottomWidget on selected file

[finetjul]

It would be great if a different widget could be specified based on the selected widget

[pieper]

small thing: in the body of the issue do you mean 'selected file' instead of 'selected widget' ; )

[finetjul]

My bad, I meant "selected file"

Note that for now, one can already disable the bottom widget: (using lambda functions)

connect(dialog, &QFileDialog::currentChanged, [bottomWidget](const QString& selectedFile) {
  QRegExp nameFilter("*.xml", Qt::CaseSensitivity::CaseInsensitive, QRegExp::PatternSyntax::Wildcard);
  bottomWidget->setEnabled(nameFilter.exactMatch(selectedFile));
});

(however, it does not work with multi selection)

[finetjul]

Also, the "Options:" label should be top aligned, and have a space before ":"