some evolutions to the API

3 different things here:

- Another correction on shared folders. Download using "file" structure didn't work on shared folders because it internally used the public link, and you can get the public link of privately shared file. I coded the direct download using the informations contained in the "file" structure

- there was a "print" in the download code. I don't feel like it's the right place for a print. Was it a forgotten debuging code or was it there on purpose ?

- While downloading, the file is now name with a temporary filename. The goal is explicitly show that the file is not usable right now (it's still downloading or result from a download that hang up). The temporary name is ".megapy-[download timestamp]-[filename]".