Ranking List

Adds graph bar for ranking list.

 On branch graphs
 Your branch is up-to-date with 'origin/graphs'.

 Changes to be committed:
	modified:   Ltt/Display.pm
	modified:   Ltt/Plotting.pm
	modified:   images/hdd_cap_by_size.png
	modified:   images/hdd_cap_by_vendor.png
	modified:   images/hdd_count_by_size.png
	modified:   images/hdd_count_by_vendor.png
	new file:   images/ltt_storage_rankings.png
	modified:   json/constants.json