title: Conditional formatting of more than one blank cells
body: <p>I have a list of names of people and 4 different trainings. 
  I would like to format my list so that if a person: </p>
  
  <ul>
  <li>has not attended any of the trainings (i.e. 4 blanks) the colour of the entire row is red</li>
  <li>has attended 1 of 4 trainings the colour of the entire row is pink (in this case one cell will have a 'date' value and the remaining 3 cells will be blank)</li>
  <li>has attended 2 of 4 trainings the colour of the entire row is orange (in this case two cells will have a 'date' value and the other 2 cells will be blank)</li>
  <li>has attended 3 of 4 trainings the colour of the entire row is yellow (in this case three cells will have a 'date' value and the other 1 cell will be blank)</li>
  <li>has attended all (4 of 4) trainings the colour of the entire row is green (no blank cells, all cells contain a date value)</li>
  </ul>