[Feature Request] Append another data file dataset to current dataset in memory

[ckgt]

Thanks for contributing to PlotJuggler. You are great! Really!

Problem description

It would be nice to be able to have an option when loading a data file to append the data in the new file to the current in memory dataset, or to load the new file entirely and forget the old data. My use case is multiple CSV files split by day. It would be nice to load the next day along side the previous when I want to continue viewing the timeseries.

Steps to reproduce (important)

• Select load new data button.
• I selected CSV file.
• No option to append data to current in memory dataset, previous day data is forgotten :(