title: Implement checkbox in NSTableView in mac application
body: <p>First of all, I searched for 3 days and have not found what I am looking for.</p>
  <p>Second point, I am VERY new to Xcode programming so PLEASE keep your answer as simple and/or detailed as possible!</p>
  <p>Inside my <code>NSTableView</code> I need the first column to be text followed by <code>X</code> number of checkbox columns with the last column to be text. The <code>X</code> number of columns is a variable based on the number of entries I read from a SQLite file.</p>
  <p>My questions are:</p>
  <ul>
  <li>How do I define at runtime what type and how many columns I have?</li>
  <li>How do I know whether a checkbox value is checked or not?</li>
  <li>How do I add rows to the tableview if I don't know the number of cells it has?</li>
  </ul>
  <p>Thanks for taking the time to answer!</p>
  <p>Best regards,
  Igor</p>