Move MaxValue in Resource Stat to constructor

[greenstack]

It doesn't make sense to require it in object initializer when it's always necessary. Also, this should simplify things by making it so that the default CurrentValue of the stat is set to MaxValue.

[greenstack]

In working on this, I don't believe that setting CurrentValue equal to the Max by default is appropriate. There are cases where the current value can and should start at zero (for example, charging up an ability). I'd rather the developer using the library specify what the starting value should be.

In tandem, I believe it makes sense to deprecate the old parameterless constructor, since a resource stat with no max makes no sense.