on resource creation : double check if contentType return same extension as file extension

[bourgeoa]

see SolidOS/folder-pane#5

on resource creation solid-ui in https://github.com/solid/solid-ui/blob/master/src/widgets/dragAndDrop.js/uploadFiles check if contentType match file extension L170-173

     var extension = mime.extension(theFile.type)
     if (theFile.type !== mime.lookup(theFile.name)) {
       suffix = '_.' + extension
       console.log('MIME TYPE MISMATCH -- adding extension: ' + suffix)

The same control is made in NSSv5.2.0 in resource-mapper.mapUrlToFile L108-110
The control should be deleted from solid-ui

[bourgeoa]

PR #147