Add USR based on a productive period (plot_biomass_catch)

[grinnellm]

Add arguments to function.

• Add productive period USR (median with lower and upper as a band) as green line and shaded area
• Highlight years used in productive period (blue)
• Productive period could be scaled to say, 90%
• Add SB_0 USR (black line and shaded area)
• Document: add USR legend (line, colour) to storyboard caption
• Add USR values to Reference points tables
• Phase plot: add green band for USR and highlight productive years
• Highlight productive period in other storyboard panels
• Add USR to "projected biomass" figure
• Add "long term average biomass" USR
• Add "proportion of SB_0" to SB_0 USR for flexibility
• Option to colour catch bars in grey