Allow overriding charges in referenced itemgroups

[ymber]

Is your feature request related to a problem? Please describe.
Currently ammo and magazine can override those values it referenced itemgroups but if charges is defined for entries in the referenced itemgroup it cannot be overridden. This means that if you want to use randomized charges sometimes and empty items other times you need a different itemgroup for each.

Describe the solution you'd like
Allow overriding charges from a higher level itemgroup as with ammo and magazine.

Describe alternatives you've considered
Reworking ammo to allow randomized ammo quantities.