[Custom Turret Controller] Add way to switch between weapons and firing modes

When a turret has multiple types of guns, for example a railgun and an artillery cannon the target lead indicator will only work with one of the two guns. Players should be able to use the toolbar or a keyboard shortcut to switch weapon and make the target lead indicator work for the selected weapon. The GUI should show somewhere the selected weapon. Additionally i suggest adding a toolbar action to select a firing mode between these two modes:

- fire all weapon of the selected type at once

- fire only one of the weapons of the selected type, then fire another one, and so on

This is useful for example for turrets with multiple railguns, so that the turret doesn't shot with all of them at once. This should also be useful for AI controlled turrets, so that they dont waste all the railgun shots at once.

The GUI should also show the selected fire mode.

There is just one problem to solve, the AI controlled turrets should be able to choose by themselves which weapon to use at any given time, since the bullet travel time is different from one weapon type to the other. Alternatively (or additionally) the weapon could be selected through the toolbar by the player even when he is not controlling the turret manually.

If you agree with this suggestion please put a thumb up. Thanks.