title: nPLot x-axis Date variable and default stacked Bar plot in rCharts
body: <p>I am using nPlot, my X-axis is Date variable, I want this to just Date as in my data 'YYYY-MM-DD', tilted vertically (90 degrees). I want nPlot show the chart stacked by default. Please help me out.</p>
  
  <p><img src="https://i.stack.imgur.com/4q41B.png" alt="enter image description here"></p>
  
  <pre><code>output$testChart = renderChart({
  testChart = nPlot(Count~Date, data = df, group = 'Category', 
        type = 'multiBarChart')
  testChart$chart(reduceXTicks = F)
  testChart$xAxis(staggerLabels = T)
  testChart$chart(stacked = T)
  testChart$xAxis(tickFormat = "#! d3.time.format('%Y-%m-%d') !#")
  return(testChart)
  })
  </code></pre>
  
  <p>and in server.R</p>
  
  <pre><code>output$mytabs = renderUI({
    tabs = tabsetPanel(
           tabPanel('Tab1', h5("Tab1"), 
                    fluidRow(showOutput("testChart"))
                    )
           )
  
  
  mainPanel(tabs)
  </code></pre>
  
  <p>})</p>
  
  <p>in ui.R</p>
  
  <pre><code>uiOutput('mytabs')
  </code></pre>