Handle or report differing chromosome labels

[arq5x]

The UCSC files that bedqc uses internally use the "chr1" convention. User files may not.

[brwnj]

users are allowed "chr1" or "1". do you have a better example that breaks it?

[arq5x]

some bed files use "Chr1", "Chrom1", etc. Might be good to just report a distinct list of chroms in the file, along with the naming schemes that are expected as part of the base report.