Create additive version of "RequiresNUnitsForMUnits" requirement

[ibboard]

Sometimes a unit will use the RequiresNUnitsForMUnits, but will need to have different amounts for different units and add those amounts together if more that one of those different unit types are taken in the army.

The best example is the Space Marines. A Chapter Master allows 1 Honour Guard. Pedro Kantor allows 1 Honour Guard. The current requirement can cope with this by putting them in the same require using the semi-colon list notation, which would allow 2 Honour Guard if both are taken (1 per Chapter Master or Kantor). Marneus Calgar allows 1 Honour Guard, but if he is taken with a Chapter Master as well then the army is allowed 4 Honour Guard, which we can't handle. The current requirement only handles "4 per Marneus or Chapter Master" (which would incorrectly allow 4 for one chapter master) or "1 per Chapter Master or 3 per Marneus" (which would only allow 1 if both were taken, the lowest of the two).