Replace replicated code with 'for' loop in StackedBarCharts

[ToonTalk]

Repeated code is harder to read and doesn't scale. The following should be clearer as a loop.

hc_add_series(name = measure_columns[1], data = stacked_bar_chart_df[,measure_columns[1]]) %>% hc_add_series(name = measure_columns[2], data = stacked_bar_chart_df[,measure_columns[2]]) %>% hc_add_series(name = measure_columns[3], data = stacked_bar_chart_df[,measure_columns[3]]) %>% hc_add_series(name = measure_columns[4], data = stacked_bar_chart_df[,measure_columns[4]]) %>% hc_add_series(name = measure_columns[5], data = stacked_bar_chart_df[,measure_columns[5]]) %>%

[charliejhadley]

We've discussed in meatspace and have agreed a compromise