title: Get records whose count matches max(count) for a category
body: <p>Given the following rows of course,section,grade,count of grades within course section:</p>
  
  <pre><code>course  SECTION  grade  gradeCount
  -----------------------------------
  1301    001      C      3
  1301    001      C+     3
  1301    001      C-     4
  1301    001      D      5
  1301    001      D+     3
  1301    001      D-     2
  1301    001      F      18
  1301    002      A-     1
  1301    002      B      1
  1301    002      B-     3
  1301    002      C      2
  </code></pre>
  
  <p>I want to get a list of course/sections with the greatest number of each grade.</p>
  
  <p>For example:</p>
  
  <pre><code>Grade|Course|Section|Count
  A | 1301| 023 | 75     // 1301-023 had the most A's, 75 of them
  B | 1301| 033 | 65     // 1301-033 had the most B's, 65 of them
  </code></pre>
  
  <p>Ties should appear in the list.</p>