#2178 Policy option to prevent changing hidden status of columns

[rgra]

It would be nice to have an option in the policy to disallow changing the hidden status of columns which are predefined in the same enforced configuration.

This is mainly of interest for the "password" column to disallow users to show a full list of all passwords in cleartext.

For reference see discussion:
https://sourceforge.net/p/keepass/discussion/329220/thread/d7911f36/