PlotPolarBar: Plots a polar bar chart of mortality causes
In bmcnellis/RSFIA: FIA Tree Mortality Analysis

TODO this

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PlotPolarBar(type = c("plots", "trees"), clear_plots = F,
  drop_no_mort = F, split = F, priv = F, only_common_ftypes = F,
  split_scale = F, return_df = F)

`type`	Either plots or trees
`clear_plots`	Logical to clear plot environment
`drop_no_mort`	Logical to drop 'No Mortality' case
`split`	Logical to split by outlier/background
`priv`	Logical to split by public/private, requires split = T
`only_common_ftypes`	Logical to exclude less common (<30 plots) ftypes
`split_scale`	Scale the split plots to be proportions of themselves?
`return_df`	Return the dataframe instead of plotting