New gene ranking method

• added new gene ranking method (SigmaFC: sum of fold-changes)
• website allows upload of either sequencing data or count data
• supports svg output of all images produced (incl. scatterplots)
• added sgRNA density (contour) plots
• output folder structure re-organized
• autmatic highlighting of top10 genes in scatterplots
• fixed minor bugs with p-value computation
• Permutation number for STARS hard-set to 10 (to avoid long computation times)