IO inaccuracies in documentation

[thompsonmj]

• scientific_name is a required input field. It may be null, but the column must be present for validation. Current docs describe it as optional, which is misleading as-is.
• input columns should mention source_id
• output files documentation implies a .resolved and .unsolved file will always be written for every resolve command input. But resolve might not include .unsolved if everything that is written goes into .resolved (misleading as-is). Also forgot to mention .forced.
• --full-rerun doesn't affect common names manifest. This functionality (or lack thereof) should be clarified, and separately decided on whether or not it should exist in some form.