Refactor "Score All"

[DavidStirling]

Perhaps someone will take this up in the future if development time is available. The current implementation of "Score All" is somewhat hacked together. As it stands creating a per-object class table causes predictions to be run twice because that optional feature was added at a later stage than the original script. The original code is somewhat messy and so there's not a straightforward way to generate both the per-image and per-object tables at the same time. It should be relatively simple to redesign the process to do everything in one pass, but it's a more major refactor than we had time for in 3.0.