title: filter = 'top' does not execute in Shiny app
body: <p>I just created the following Shiny app using <code>DT</code>. My problem is that <code>filter='top'</code> does not actually seem to execute. Is there a problem combining <code>checkboxGroupInput</code> and filter from DT? I was hoping to be able to add as many filtering options as possible. </p>
  
  <pre><code>ui.R
  
  library(shiny)
  
  
  shinyUI(pageWithSidebar(
    headerPanel('Database'),
    sidebarPanel(
  
      p('Welcome to the Database.'),
  
      p('(1) Use the dropdown menus to select a category, type, or  manufacturer.'),
      p('(2) Use the checkboxes below to add or remove information from the table.'),
  
      checkboxGroupInput('show_vars', 'Information:', names(Foods),
                         selected = names(Foods)),
  
    ),
    mainPanel(
  
      fluidRow(h1('A Server-side Table')),
  
      fluidRow(
        column(9, DT::dataTableOutput('x3')),
        column(3, verbatimTextOutput('x4'))
      )
    )
  )
  )
  
  server.R
  
  library(shiny)
  library(DT)
  
  shinyServer(function(input, output, session) {
  
    # server-side processing
  
    output$x3 = DT::renderDataTable(Foods[, input$show_vars, drop = TRUE], server = TRUE, 
                                    options = list(pageLength = 5, autoWidth = TRUE,
                                                   columnDefs = list(list(width = '200px', targets = "_all"))
                                                   , filter = 'top'))
  
    # print the selected indices
    output$x4 = renderPrint({
      s = input$x3_rows_selected
      if (length(s)) {
        cat('These rows were selected:\n\n')
        cat(s, sep = ', ')
      }
    })
  
    }
  )
  </code></pre>