Allow unordered conditions

[halleysfifthinc]

TrialConditions currently requires the condition names to be given in the order they must appear in filenames/paths. Originally, the single regex used to match all conditions forced a strict ordering, but the new(ish) extract_conditions could be modified to allow a more relaxed ordering. One implementation idea to control scope/complexity would be to add a wrapper type (e.g. Unordered or something) so that the relaxed ordering could be limited to a few conditions, e.g. [:subject,Unordered([:arms, :kind])].