Cell,Document,Grid: Regularize/cleanup coord operations
CombinedModelGrid: Refactor into gridlocate from geolocate
GridLocate/CombinedGrid: Create separate grid for each input corpus, add ID's to grids, cleanup #non-empty-cell calc
SphereCoord/TimeCoord/etc.: Handle coordinate utility functions through a type class not a mixin
Evaluation: Clean up how to specify eval file(s) and better document how to specify training data
WIP: Allow for unknown correct cell/coord when eval
WIP: Allow for unknown correct cell/coord/rank when eval