Use an extension for CSV exports

[maxpatiiuk]

Currently, CSV exports are named as csv. This is recognized by the system as a file without an extension and the user can get an error message about the unknown format and a prompt to select an associated app in some systems (Windows,...). Also, when importing this file in other programs, it is going to be filtered out because it does not have a requested extension.

A good solution would be to add a name to those files (e.x. data_export.csv