Sample order is not preserved for merged samples

[nsheff]

In version 0.32.0 we introduced a new feature where you could have non-unique sample names, which would be merged into one sample automatically.

This works, but it re-orders the samples; merged samples come at the end of the table instead of in their original position.

I suppose the two rows in the table that share a name could be in different places, so maybe it's hard to decide where to put the merged sample in the merged table. But often they are next to one another and in that case it seems like they should go there, where they originally were. I think it would be safe to simply put them in the spot of the first instance of the duplicate.