[BUG] Converter dialog does not store the working directory

[MBartkowiakSTFC]

Description of the error Converter dialog is an instance of ActionDialog. When multiple widgets are asking for input files, the file dialog starts in the MDANSE_GUI working directory every time.

Describe the expected result The dialog should store the path of the first input file, and use it when looking for the next file. The ActionDialog used for analysis runs already does it most of the time.

Describe the actual result See above.

Suggested fix A better way of storing the current path and recently used paths needs to be implemented.

Additional details Add any other context or screenshots about the feature request here.