Warn on stupid sample names

[dpryan79]

It would be quite nice if users received a warning if they specify completely stupid names for their samples. A stupid name would be any of the following:

1. A 1-2 digit number
2. A single letter followed by a 1-2 digit number (e.g., A1, B12 and C6)

The warning could be, "You appear to have chosen uninformative sample names. You are strongly encouraged to choose sample names that are actually meaningful (e.g., foobar_WT_1 and foobar_KO_1). Using uninformative sample names is very likely to lead to problems and delays when you submit your data to an archive prior to publication!."

We shouldn't be preventing people from shooting themselves in the feet, but this will at least warn them that they're doing so.