Config file paths for realm and app config need to have different errors

[papafe]

At the moment the code path for getting the default path for Realm and App is the same, and thus the exception for both is the same when the path is not writable, with message "Couldn't determine a writable folder where to store realm file. Specify absolute path manually."
We need to have two different string messages, so that developers can understand which of the two is causing issues.