Fixed overly high default value for minQuality of window filter, added its range check (it is converted to Byte after reading the JSON) in Application's validate()

Reverted filtering behavior of sequences containing 'N' symbols: from the current rejection when at least one 'N' is present to the old behavior of rejecting only  sequences  comprised exclusively of 'N's. Since in practice most sequences contain lots of evenly dispersed 'N's, this was preventing the assembler from building any contigs at all.

Removed the accidental change in format of one of log messages introduced in a previous commit.