Partition Manager should only use database queries, not partition names, for calculations

[jcjones]

This is a breaking change and will need a significant version increase.

This is an optimal solution to #19 and #46.

[jcjones]

This also will help some with #42 , in that when we stop caring about names of partitions then naturally we'd want to be able to adjust positions of partitions if they're mispredicted.