renderDropdownMenu: Create a dropdown menu output (server side; deprecated)
In rstudio/shinydashboard: Create Dashboards with 'Shiny'

This is the server-side function for creating a dynamic dropdown menu.

1	renderDropdownMenu(expr, env = parent.frame(), quoted = FALSE)

`expr`	An expression that returns a Shiny tag object, `HTML()`, or a list of such objects.
`env`	The parent environment for the reactive expression. By default, this is the calling environment, the same as when defining an ordinary non-reactive expression. If `expr` is a quosure and `quoted` is `TRUE`, then `env` is ignored.
`quoted`	If it is `TRUE`, then the `quote()`ed value of `expr` will be used when `expr` is evaluated. If `expr` is a quosure and you would like to use its expression as a value for `expr`, then you must set `quoted` to `TRUE`.