Allow passing of colour table when deploying shiny apps

[andrew-MET]

By default colours are assigned in shiny_plot_point_verif() from a fixed colour palette, taking the colours in order. The user can then change the colours in the app, but if they have to do this every time that can be a bit of a hassle! plot_point_verif() allows the user to pass a data frame with key value pairs for 'mname' and 'colour' to control which fcst_model gets which colour.

This functionality should be extended to the shiny app with the option to pass a colour table via shinyOptions. Will need to take into account what to do if not all mnames are in the colour table - currently plot_point_verif() just resets the entire colour table.

Could also add bookmarking so that a user can save their colour choices for next time.