Make add require confirmation for unadvisable actions

Make add require confirmation for unadvisable actions

Deleting a country in state STAT_SANCT, STAT_ACTIVE or STAT_GOD is
risky, because any references to this country become dangling, which
makes ef_verify() unhappy.  For a reason: we may well have code that
isn't prepared for dangling references, and breaks.

Replacing a country that is being used is risky, because it can get us
into weird states.  For instance, replacing a player by a visitor can
result in a visitor that owns stuff.