let ConfigLoader construct IReadClassifier,

and use IReadClassifier in BamSummary to build flag distributions (mate
pair coming soon)
remove commented code
rename ARP flags for abnormal insert sizes

ARP_FR_small_insert => ARP_SMALL_INSERT
ARP_FR_big_insert   => ARP_LARGE_INSERT
add description() method to BamReaderBase

this way the region limited bam reader can say something about its
region
give a better error message when no reads are found in bam regions
move ReadClassifiers to config lib to avoid circ. dependencies