Dropzone/file uploads improvement

[texx00]

Should add the possibility to upload multiple files at once.
May be possible to cloase the modal and use a toast with a progress bar at the bottom of the screen. After putting the files.
Should also consider to load the last drawings instead of reloading the entire page with ajax/sockets
Should also fix the upload progress bar after bootstrap introduction

[texx00]

The dropzone is now loading also multiple files at once.

The use of react fixes: Should also consider to load the last drawings instead of reloading the entire page with ajax/sockets

Still can improve the visualization of the files while loading (in the upload modal or by adding a toast at the bottom with the progress bar)