selectInput to specify legend position

Usage

addLegendUI(
  id,
  label = "Legend Position",
  choices = c("none", "topleft", "topright", "bottomright", "bottomleft")
)

id: module id
label: label of button
choices: choices e.g. "bottomright", "bottom", "bottomleft", "left", "topleft", "top", "topright", "right" and "center"