Pop-up windows when loading Layout with multiple csv files

[ellenanth]

Thanks for contributing to PlotJuggler. You are great!

I'm making an application that uses PlotJuggler for data visualization. The application creates layout files and csv files dynamically and opens PlotJuggler through the terminal.

When loading PlotJuggler using a custom layout that contains multiple csv-files, the user is asked for each csv-file if the previous data should be removed.

I think it would be more logical when loading a custom layout on startup, this is not asked.