detect and enforce selected tab for dynamic sidebars

[bborgesr]

This is very simple fix, just running ensureActivatedTab() after renderMenu (renderValue method) is called. This allows for the correct tab to be selected for dynamic sidebars (closes #87, closes #71)

Here's an example app, from #71:

library(shiny)
library(shinydashboard)

ui <- dashboardPage(
  dashboardHeader(title = "Dynamic sidebar"),
  dashboardSidebar(
    sidebarMenuOutput("menu")
  ),
  dashboardBody(tabItems(
    tabItem(tabName = "dashboard", h2("Dashboard tab content"))
  ))
)

server <- function(input, output) {
  output$menu <- renderMenu({
    sidebarMenu(id="mytabs",
      menuItem("Menu item", tabName="dashboard", icon = icon("calendar"))
    )
  })
}

shinyApp(ui, server)

[bborgesr]

closing in favor of #199