Add a Template container type with a "custom point value" optional field

[Xain3]

Right now, there is to my knowledge no way of modifying the default container behaviour (sum the points of all the included traits/skills/items), except for selecting the Alternative Abilities type, which applies its own modifier.

This happens also in the case if template containers, even when we do actually know the value, or the value range, that the container is going to take.

It would be great if we could add a Template container type, where the user could chose to specify a custom point value, a range of values (although I am not sure how this could be handled), or the average of the values in the container multiplied by X (defaulting to X=1).

This would help with templates point coats as currently it is pretty hard to keep track of them!