Uploading a folder of images without selecting them all

Currently, this application is using standard File input API. This forces the user to select all images to import, and cannot retrieve files recursively in folders.

We know however that Chrome is able to do so for google drive, so there should be a way. If anyone wants to dig into that, the code that deals with loading multiple files is in client/src/Packages/Button.elm:

• loadMultipleFilesInput: function generating the File input button to load images.
• loadMultipleFilesEvent: function decoding the list of files loaded by the input.

An alternative solution would be to be able to load a zip containing all images. This implies that the unzipping would have to be done in the browser.