code to plot metrics distribution - colour by gender and population (Feature/plots enhancement)

[justinjj24]

• Distribution plot of ALN and VCF QC metrics
• [x] median absolute deviation code updated as mad = np.median(np.abs(merged_dft[col] - median)) instead of mad = np.mean(np.abs(merged_dft[col] - median)).
• [x] colour by gender male-blue/female-red
• [x] colour by Superpopulation_code - AFR/SAS random colour

[mhebrard]

Switch to #38