New feature: Use closest read length

It is possible to instruct CheckQC to use the closest read length if the read length of the run is not found in the config. In case of a tie between two read lengths, the longer read length (with stricter QC criteria) will be used.

Usage:
$ checkqc --use-closest-read-length <RUNFOLDER>

This parameter can be supplied to the webservice as a query argument:
curl -s -w'\n' localhost:9999/qc/170726_D00118_0303_BCB1TVANXX?useClosestReadLength | python -m json.tool