Remove cache-control switch from private to public

[sbrunner]

This is not working with intranet detection

To make it working (with intranet detection and reverse proxy cache) without the possibility of cache pollution, we should:

• Disable it for the loginuser end-point.
• Be sure that we have the user or roles in the query string, And verify them in the Pyramid view.

[ger-benjamin]

Could this be a breaking change ? Should we add documentation about that ? Or it currently doesn't work ?

[sbrunner]

@ger-benjamin I will add a message in the changelog to be transparent, this can't be associated to a breaking change :-)