title: levelplot: how to add space between colorkey and x-axis label
body: <p>I am trying to use <code>levelplot</code> to plot a simple Digital Elevation Model (DEM). </p>
  
  <p>Here is my code:</p>
  
  <pre><code>r1 = raster("ned10dem.tif")
  e = extent(460000,480000,4555000,4567500)
  rr1 = crop(r1,e)
  p = levelplot(rr1, scales=list(x=list(at=seq(450000,480000,4000))),
                margin=F, cuts=200,
                col.regions = terrain.colors(350,alpha=1), 
                colorkey=list(space="bottom"),
                xlab="Easting(m)", ylab="Northing(m)")
  plot(p)
  </code></pre>
  
  <p>The plot ends up looking like this:</p>
  
  <p><img src="https://i.stack.imgur.com/jS5Sy.png" alt="levelplot"></p>
  
  <p>What I cannot figure out is how to increase the space between the colorkey and the x-axis such that the colorkey does not cover the x-axis label. </p>