Add default copy constructors/assignment operators to json (de)serializers.

To please the the higher compiler Being Whom we revere.
Add default copy constructors/assignment operators for player_activity
Add default copy constructors/assignment operators for inventory

Removes the implementations of the assignment operators. Those are strange anyway.
Add default copy constructors/assignment operators for item
Add default copy constructors/assignment operators for point
Add default copy constructors/assignment operators for clZones
Give the inventory class a default constructor

members of the class initialize themselves, the boolean is initialized explicitly.
Remove some pointless copy constructors

The compiler generated defaults do the same and don't prevent the other automatically creation of assignment operator.
Merge branch 'more-compiler-generated-things' of github.com:BevapDin/Cataclysm-DDA