App controller for sortmerna mapper

+ doc strings edited.
This is explained in the sortmerna -h page, but I've also added a small explanation in brokit. Basically, --blast 3 will output the traditional m8 tabular format + 2 extra columns for the CIGAR string and the query coverage. The other possible choices are 0: pairwise alignment, 1: m8 and 2: m8 + CIGAR string. By setting to 3, users will have both 1+2. Option 0 produces a lot of data and I don't think it will be useful in OTU-picking. However, I've added the possibility to change it here in sortmerna_map().