Idea for the report table: A mini-plot that shows where Ns are in the assemblies

[RaverJay]

Could also include warnings when N stretches are in important regions, e.g. the spike protein

As any mutations/deletions/insertions are just omitted when the corresponding region isn't covered enough, this might give a better overview what to expect.

Not sure on the details - and no idea where to find the time :D