Code review comment for lp:~marcustomlinson/unity-api/lp-1552082

The locking here is at the wrong level of abstraction, I believe. It is not necessary to lock at this level because there will be many cases where the writer and reader are the same single process.

The locking needs to be added at the level above, which knows whether a particular file might be accessed concurrently.

We already have locking in SettingsDB in scopes API. The locking needs to be moved in to the shell, to do the equivalent of what QSettings does.