title: Switching between menuSubItems in shinyDashboard
body: <p>I'm trying to set up a shiny app using shinydashboard, and for the most part, having good luck.  However, I'm running into a quirk with sidebar behavior that I think is avoidable, but haven't found how yet.  </p>
  
  <p>Below is a small example that reproduces the problem I'm having.  Basically, there are two sidebarMenus - Menu One and Menu Two, each with two menuSubItems.  Switching subitems within a menu item works fine. So, if I wanted to switch from subItemOne to subItemTwo, no problems.  I can do that all day.  </p>
  
  <p>I can also switch to subItems across menus, such that jumping from subItemOne to subItemThree, that's fine.  The problem lies in trying to switch back.  If subItemOne is selected, and I try to go to subItemThree and <em>back</em> to subItemOne, I can't do it.  I have to go to subItemTwo, then I can open SubItemOne.</p>
  
  <p>Is there a way to correct this setup such that I could jump directly from subItemOne to subItemThree (or two and four) and back again?</p>
  
  <pre><code>library('shiny')
  library('shinydashboard')
  # Sidebar #############################
  sidebar &lt;- dashboardSidebar(
    width = 290,
  
    sidebarMenu(
      menuItem('Menu One', tabName = 'menuOne', icon = icon('line-chart'), 
          collapsible = 
              menuSubItem('Sub-Item One', tabName = 'subItemOne'),
              menuSubItem('Sub-Item Two', tabName = 'subItemTwo')
              )
    ),
  
    sidebarMenu(
      menuItem('Menu Two', tabName = 'menuTwo', icon = icon('users'), 
               collapsible = 
                 menuSubItem('Sub-Item Three', tabName = 'subItemThree'),
               menuSubItem('Sub-Item Four', tabName = 'subItemFour')
      )
    )
  
  )
  # Body #############################
  body &lt;- dashboardBody(
  
    tabItems(
      tabItem(tabName = 'subItemOne',
              h2('Selected Sub-Item One')
      ),
      tabItem(tabName = 'subItemTwo',
              h2('Selected Sub-Item Two')
      ),
      tabItem(tabName = 'subItemThree',
              h2('Selected Sub-Item Three')
      ),
      tabItem(tabName = 'subItemFour',
              h2('Selected Sub-Item Four')
      )
    )
  )
  # UI #############################
  ui &lt;- dashboardPage(
    dashboardHeader(title = 'Test', titleWidth = 290),
    sidebar,
    body
  )
  # Server #############################
  server &lt;- function(input, output){
  
  }
  
  shinyApp(ui, server)
  </code></pre>