Warn user if prep info file contains duplicate samples

If there are two samples (say, sample 1) that are run twice in the same prep run, then gail has to add a new sample in the Qiita metadata, and give it a new name (like sample 1B) but with duplicate info to sample 1 otherwise. Then she has to go into the prep info file and change one of them to be called sample1B. In fact, she prefers to rename the original sample in both Qiita and the prep file (e.g. sample1A and sample1B) to reflect that NEITHER is known to be "the more right one".

To remind users that they need to do this step, she would like a warning to be shown to them at the time they download a prep file if that prep file contains duplicate samples. The warning should tell them they will need to make these manual modifications to both Qiita and the file itself.