title: plotly: range slider on x-axis (date) with custom start / end date
body: <p>Is there an option to use the <code>rangeslider</code> option in the <code>plotly</code> package so that you add a slider AND specify which range is the default. Right now, the following code adds the slider but by default the entire range of dates is selected. </p>
  
  <pre><code>library(plotly)
  
  df &lt;- data.frame(Date = seq(as.Date("2016-01-01"), as.Date("2016-08-31"), by="days"),
                   Value = sample(100:200, size = 244, replace = T))
  
  p &lt;- plot_ly(data = df, x = Date, y = Value, type = "line") %&gt;%
    layout(xaxis = list(rangeslider = list(type = "date")  ))
  p
  </code></pre>
  
  <p>I'd like to be able to specify the initial range - for instance, show only the last month and allow the user to extend the range if he so wishes. The documentation seems to suggest that there are no such option and I'd rather not go the custom javascript way.</p>
  
  <p>Any ideas?</p>