R1:23b835b64731

Begin lifting column layout logic out of ColumnPositionQuery

Summary:
Ref T10010. This is a precursor to D15171, which I'll eventually rebuild on top of these changes.

Currently, ColumnPositionQuery does a lot of "column layout" stuff that's very similar to the Milestone/Subproject stuff that needs to happen in D15171. The current approach there ended up splitting this layout stuff across two unrelated classes (ColumnPositionQuery + BoardViewController), neither of which is a particularly great place to…