Add feature to consider the same type of item made from different materials a Similar Stack.

[ubergarm]

This is basically #7 but now I understand it:

As is, a Similar Stack Limit of 1 will still allow say 1x plainleather cowboy hat and 1x cloth cowboy hat to both be in the same stockpile even though they are both cowboy hats.

So this ticket is to add a feature configurable in the settings to consider them similar.

[ubergarm]

I finished this code but haven't prep'd for release yet