Improve file upload dialog

[spaenleh]

File upload dialog can be improved to allow better user feedback.

• [x] "Done" button should either be removed OR close the dialog to let users know that the operation was performed successfully.
• [ ] Height of the file upload dialog should be adapted to the height of the modal.
• [x] #846

[pyphilia]

The done button disappear in that PR https://github.com/graasp/graasp-builder/pull/1295