merge gridfs files with current implementation

[OlivierJM]

in V2 we are using GridFs to manage files in MongoDB this allows us to easily sync files, it would be nice to have a merging other GridFS files with mongoose implementation that we have, we could then provide a way of importing from like a dumped mongodb.
Basically what needs to be done on this is to make the file upload work nicely with GridFS
V2 can be found here https://github.com/SparkEdUAB/sparked