Add ability for a Template trait container to accept a range of point value totals

[SilntObsvr]

Currently, if you create a trait container in a Template it will allow the user to select various traits to add up to the container's point value -- but this must be an exact match, so if I want, say, 20 points from a list of traits, I can't (practically) include a trait that's 3 points per level, as some values wouldn't be compatible with other 5/10/15 point traits in order to produce exactly 20 points.

I'd suggest allowing this type of container to accept a range of values, specified the same way container point values are currently specified, but with "minimum points" and "maximum points" and allow the container to close with any point value in the specified range.

[Xain3]

Might be merged with #878 ?