You can clone with
HTTPS or Subversion.
Offline mode is the only thing missing from this app. I will try to see how the chrome extension works, maybe a port to safari could be done.
As far as I can tell the extension only allows unlimited local storage for the site. So I'm thinking that the site actually checks for how much local storage it has and if it is enough it turns on the offline mode.
At some point I contacted dev team of Deezer and asked them question about it. It looks like there are dependency on IndexedDB that prevent this function to work on Safari (and therefore basic framework on OS X). There is possibility to include Google Chrome rendering engine instead of Safari's, but this would take too much work to be worth it.
I understand, I also got a response from the Deezer dev team, they said they are working on a native mac os app that will be available in a "couple of months"
So, until then will use the app without offline mode.