AP use confusion

[KV7]

The Soviet T-28 M1938 seems to never fire its 10 AP rounds; even though the main gun does 6 pen for AP and only 2 for HE.

I tried kludging it by giving it two guns; one only with HE and one only with AP so the user can select the firing round by turning off the relevant fire slot (this trick can be nice for gunships too to allow select fire for the rockets - as you can choose to fire HE rockets to button the tank then come in close to use the AP)

This fixes the unit as it can now fire the AP and kill flimsy early war Polish/Finnish/German tanks.

For some reason the BT CS tanks manage to fire their AP rounds and to good effect.