title: Smart table: conditional st-sort attribute in ng-repeat
body: <p>I am using Angular Smart Table and it is pretty good, but i faced with problem related to sorting:</p>
  
  <p>let's assume that i have some columns definition and for each column i have information whether i can sort by this column or not:</p>
  
  <pre><code>$scope.columns = [
      {
          id: "id",
          sortable: true
      },
      {
          id: "type",
          sortable: false,
      }
  ];
  </code></pre>
  
  <p>In my html file i want to declare table headers with ng-repeat to avoid stupid refactoring when something in columns definition is changed. Somethig like that: </p>
  
  <pre><code>&lt;table class="table" st-table="records"&gt;
   &lt;thead&gt;
    &lt;tr&gt;
     &lt;th ng-repeat="column in columns"&gt; {{ column.title }} &lt;/th&gt;
    &lt;/tr&gt;
   &lt;/thead&gt;
   ....
  &lt;/table&gt;
  </code></pre>
  
  <p>So my question is: how can i set attribute "st-sort" only for those columns, for which <strong>column.sortable</strong> is true? 
  I tried to use custom directive that adds this attribute depending on <strong>column.sortable</strong> and it actually adds it, but st-sort not works in this case (may be because this directive compilation is happening after table compilation, i have no idea...)</p>