title: ggplot2 issue with facets and turning off clipping
body: <p>It used to be possible to put text on plot margins by turning off clipping. In ggplot2_2.2.0 this doesn't seem to be possible anymore in plots that use facets (but still works if no facets are used). I've posted an issue <a href="https://github.com/tidyverse/ggplot2/issues/1929" rel="noreferrer">here</a> but it has not been addressed yet. Any ideas for workarounds in the meantime would be greatly appreciated! </p>
  
  <p>Here is a minimal (non-)working example:</p>
  
  <pre><code>library(ggplot2)
  library(grid)
  
  df.plot = data.frame(x = 1, y = 1, facet = 'facet', stringsAsFactors = F)
  df.text = data.frame(x = 1, y = -0.3, label = 'test', facet = 'facet', stringsAsFactors = F)
  
  p = ggplot(df.plot,aes(x = x, y = y))+
    facet_grid(~facet)+ # 'test' is only printed outside of the plot if faceting is turned off
    geom_point()+
    geom_text(data = df.text,aes(x=x,y=y,label=label))+
    coord_cartesian(xlim = c(0, 2),ylim=c(0,2),expand=F)+
    theme(plot.margin=unit(c(2,2,2,2),"cm"))
  gt = ggplot_gtable(ggplot_build(p))
  gt$layout$clip[gt$layout$name=="panel"] = "off"
  grid.draw(gt)
  </code></pre>