Add drag and drop files

[ostatni5]

No description provided.

[grzanka]

Try following test:

1. Open UI as it is on your branch
2. Open yaptide UI editor, and load a project from following JSON: https://gist.githubusercontent.com/grzanka/cd47cacce2f6d5986397630d76580d11/raw/e6ca6a23fbae78b04ddcfaf2582bc7c3f972e995/2022let_plan2.json
3. Go to "Input files" and click "Generate from editor". Several files will appear there, one of them will be sobp.dat.
4. Now, on Windows, I find some directory with 4 usual input files (beam.dat, geo.dat, detect.dat and mat.dat). I drag and drop these files into the yaptide UI.
5. I would expect that sobp.dat disappears, but thats not the case, it is still there.

[grzanka]

Another exercise:

1. Generate input files as in the comment above
2. Clear all the files
3. Move just one (mat.dat) files into drag and drop
4. Suddenly all the files all populated, despite the fact I've cleaned them
   https://user-images.githubusercontent.com/7374733/230183049-4777c271-6c23-4e28-8173-553a0ee12ad3.mp4

[grzanka]

I am happy to stay with the situation that uploading new files is not removing the old files. But in such case I would like to see a good option to remove only part of the files or all of them. Cleaning seems not to work properly

[grzanka]

@Derstilon please review as well, to me it looks OK