user can upload files by dragging them from desktop file manager

app/components/button/upload.js

app/components/choice_field/index.hbs

app/components/choice_field/index.js

app/components/commander/index.js

app/helpers/is_equal.js

app/modifiers/droppable.js

app/services/current-user.js

app/services/preferences.js

app/services/uploader.js