v2.5.0 - New tools and reduced dependancies

Added detectExtremeDepth.pl, see wiki page Hi seq depth regions.

Bugfix/optional functionality in bam_stats.pl

• Fixes long standing bug in bam_stats.pl -plots option which failed when it encountered
  empty default readgroup '.', used when a read has no RG_ID attached.
• Allows PCAP-core to be installed without support for the bam_stats.pl -plots option.
  Removes dependancy on GD::Image and Math::Gradient. Functionallity preserved provided
  if modules found in PERL5LIB, otherwise warnings.