[POC] Data mapper fs

PoC HERE : ```test/adapter.php```
ok, but as a purely end user, it would be strange to me to give a File, in order to have a file.
when I open a file in my browser, I don't give him a file, but a path (a key).
It feels more natural.

I'm wating from the fs (and thus, the adapter) to actually "fetch" me a file (for us, using the fileFactory) .
So every adapter would have a fileFactory to do so.