Allow any kind of file extension

## The problem

I've got some parquet files that don't have any extension. I would like to open those files through `Edit > Import` or just by dragging and dropping, but I can't and I have to rename them adding `.parquet` at the end of their names.

## Proposed solution

- In the file picker window add an option that accepts all kind of files
- When a file gets dropped on the window, pandasgui tries to open it as a known file type, if it fails it shows a message saying like: 'Unsupported file format'