title: ngTable tooltip (title attribute) does not show data values
body: <p>In this <a href="http://plnkr.co/edit/8abiLrqa6hAoFSySgaLT?p=preview" rel="nofollow">plunk</a> I have an ngTable with two columns. When I hover over the data, the tooltip shows the column name instead of the value. This is because the <code>title</code> attribute of <code>td</code> is set with the column name. How to fix it to show the actual value?</p>
  
  <p>HTML</p>
  
  <pre><code>&lt;table ng-table="tableParams" class="table table-bordered table-hover"&gt;
      &lt;tbody&gt;
          &lt;tr ng-repeat="u in data"&gt;
                  &lt;td title="u.uid"&gt;{{ u.uid }}&lt;/td&gt;
                  &lt;td title="u.ugr"&gt;{{ u.ugr }}&lt;/td&gt;
          &lt;/tr&gt;
      &lt;/tbody&gt;
  &lt;/table&gt;
  </code></pre>
  
  <p>Javascript</p>
  
  <pre><code>var app = angular.module('app', ['ngTable']);
  app.controller('myCtl', function($scope,NgTableParams) {
  
        $scope.data = [ 
          { uid: 'User 1',ugr: 'Group 1'},
          { uid: 'User 2', ugr: 'Group 2'}
        ];
  
        $scope.tableParams = new NgTableParams({dataset: $scope.data});
  
  });
  </code></pre>