title: Add x and y axis to all facet_wrap
body: <p>It is often desirable to minimize ink in a plot.  I have a faceted plot (<code>facet_wrap</code>) and would like to remove as much ink as possible yet maintain readability.  I have set it up as I'd like except the x and y axis is not present for the facets (subplots) unless on the far left or bottom.  With so much ink removed I believe the eye needs these cues and am asking how to put the x and y axis in all plots within a <code>facet_wrap</code>.  Below is my code thus far, the current output and the desired output (red lines are the desired add in):</p>
  <pre><code>library(ggplot); library(grid)
  
  ggplot(mtcars, aes(mpg, hp)) + 
      geom_point() + 
      facet_wrap(~carb) +
      theme(panel.grid = element_blank(),
          panel.background = element_rect(fill = &quot;white&quot;, colour = &quot;black&quot;), 
          panel.border = element_rect(fill = NA, colour = &quot;white&quot;), 
          axis.line = element_line(),
          strip.background = element_blank(),
          panel.margin = unit(2, &quot;lines&quot;))
  </code></pre>
  <p><strong>Current Plot</strong>
  <img src="https://i.stack.imgur.com/uSWgh.png" alt="enter image description here" /></p>
  <p><strong>Desired Plot</strong>
  <img src="https://i.stack.imgur.com/cqUXa.png" alt="enter image description here" /></p>