Create upload module

The upload module handles some common jobs related to dealing with file
uploads. For now, it has a function you can call at startup to ensure
your preferred upload temp directory exists and a middleware to make
sure each of the temp files created by multer have been deleted.
Add deleteOriginal option to FileStore

This option can be set on the whole FileStore object, or when calling
store(). It tells it whether or not to delete the original file when
storing it. Defaults to true.