Bug 1067384 — Handle topic specific SimplePushURLs + link SP URL to Session

https://bugzilla.mozilla.org/show_bug.cgi?id=1067384
This was to be future proof, but my goal was to ignore not JSON content keys. If it is not JSON, we don't care about it so why should we log that?
We can also not try{} catch{} here as we are creating the keys but in case something happen, we will have to delete the broken key ourself.