Add plot improvements

[KristinaRiemer]

For relative weight plot:

• Change to points only
• Replace percentiles with SE error bars

Others:

• Change Gabelhouse x-axis label to "Proportional size distribution"
• Remove unnecessary legend from frequency plot
• Add captions to all plots
• Comparison frequency plot add UU box
• Display calculated UU numbers (e.g., on blue bars)

[KristinaRiemer]

Closed w/ #31