Status field for seqrun should have defined values

[pekrau]

Which statuses?
Which transitions?
Any constraints?

Important: some status must be defined for which the alignment_coverage value is summed up for the libprep. If a seqrun is at first believed to look nice, it is included. But it must be possible to exclude it later, if found to be deficient in some way. This can be done by setting the status to "rubbish" or something that shows it has been done, but should not be included in accumulated results.