InstData Import/GMT Picard: add downsample ratio mixin
Downsample Ratio: update the downsample ratio mixin to be like the objects with API
GMT Picard: make _downsample_ratio_is_required class method
GMT Picard/InstData Import Downsampl Ratio: made separate class for required downsample ratio; updated errors; added tests
InstData Import: rm comment from basic bam downsample test
Merge remote-tracking branch 'origin/master' into downsample-ratio-mixin

Conflicts:
	lib/perl/Genome/InstrumentData/Command/Import/Basic_bam_downsample.t
Merge pull request #27 from ebelter/downsample-ratio-mixin