Add reference genome coverage to the report about porecov

[hoelzer]

Okay, thought about this again and I agree. Basically with that we also have a proxy of how well the Wuhan reference genome is covered by reads. So that's fine.

The only other thing is: a mean/median coverage value bc/ I think this is needed often for submissions to databases such as GISAID, ... or?

[replikation]

the genome is 20x masked by "N" so the reconstructed genome itself represents > 20x coverage
and the identity is listed in the report also the number of mismatches. So not sure what the metric would give as useful feedback for the report (just want to avoid adding a barrage of infos)

[replikation]

all this thing should be in the president qc data I think. but would be to much for just the report