Multiple CSV Files import - Feature request

So I have been working with CSV's using this program for a couple of weeks now, which is great by the way. There is one thing however that I believe would help people who deal with multiple CSV files. Importing each file individual is a pretty tedious process, in my opinion and I think being able to mass import the files would be a great feature.

**Describe the solution you'd like**
One solution that I would find most useful, is adding a feature to import multiple files that have an option to either automatically concatenate all of the data from the files or have a selection on the left hand side allowing you to select the CSV files that you would want to concatenate for that widget.

**Describe alternatives you've considered**
Alternative solutions that I had thought about trying is to concatenate all of my CSVs down into one file, however it would be nice to have a solution that does not involve me physically changing the CSV files or having to create a new file all together.

**Additional context**
The screenshot below shows a current layout using the individual "CSV File Import" widgets, then me doing some magic towards them and then concatenating:

but what would be nice is to instead, have a layout where the concatenation process is dealt within the CSV import, for example:


Great work with Orange so far,
James Dibnah.

Review the existing CSV File Import widgets and the current concatenation workflow described in the issue, then identify the relevant import and widget entry points. Done means multiple CSV files can be imported, optionally selected for concatenation, and used without manually creating a combined file.

Written by the indexing model from the issue text.