[shareit] Add a default value for chunk size to 20M

- comment line tools.LOG_DEBUG.Println("Received ", read_size, "bytes")
[shareit] sqlite: add password and NbDownloads in database
[shareit] add update share link and delete sharelink
[sahreit] salite: fix update account function
[shareit] add debug mode (by default not activated)

- remove command from database
[shareit] remove duplicated comments
[shareit] add get_info command
Close file descriptors + use the io.Copy Method instead of doing it ourself
Add some profiler