Import Logic Modified Slightly

When performing an [[import]] operation, and importing a folder of text files, Notenik will now suspend its usual requirement that all desired fields be already defined for the Collection, and will instead add any new fields found in the input source, but not already defined for the Collection. This is consistent with the general principle to “Be conservative in what you do, be liberal in what you accept from others” (often referred to as Postel’s Law).