Don't draw the feature coverage plot if there aren't any features.
Rename QualityDistribution to MappingQualityDistribution.  Change the
output to the maximum observed value rather than the theoretical
maximum.
Change the bar graph to have continual bins.  Remove background shading.
Remove code intended for multiple data set display since it can only
really show one.
Merge branch 'master' of https://github.com/s-andrews/BamQC.git

Conflicts:
	uk/ac/babraham/BamQC/Modules/MappingQualityDistribution.java
	uk/ac/babraham/BamQC/Modules/ModuleFactory.java