Adding, removing and then re-adding the same file doesnt work.

[MarkusHenkel]

Description

To Reproduce
Steps to reproduce the behavior:

1. On the initial page upload any file (wiggle, gff or mastertable)
2. Remove the file you just uploaded by pressing the remove button
3. Upload the same file you just removed and notice that it doesnt show up even though you could select it in the explorer and that you wont be able to start the prediction.

Expected behavior
Uploading, removing and then uploading that same file again should work just like it does for varying files.