generalise manager

The config file manager can be generalized to mess with all the config file in profile. 
Will be usefull for jupyterdrive.
So you'd need to override this to mess with server or kernel config, right? Because the files are named `ipython_{section}_config.json`.

Also, we should be a bit careful how we use this, because kernel and server config may be in different folders after the IPython/Jupyter split.