title: `sortProperty` attribute is not sorting `sap.m.table`
body: <p>I'm trying to add a sorting feature on each column of a table. I have inspected the example provided by SAPUI5 explored here: <a href="https://sapui5.hana.ondemand.com/sdk/explored.html#/sample/sap.ui.table.sample.Sorting/preview" rel="nofollow noreferrer">https://sapui5.hana.ondemand.com/sdk/explored.html#/sample/sap.ui.table.sample.Sorting/preview</a></p>
  
  <p>Specifically I added a <code>sortProperty</code> attribute to the column element in my XML-view (see <code>Qty</code> below), but I don't see any sorting functionality nor any sorting arrows like in the example provided. Could someone examine what I'm missing here?</p>
  
  <pre class="lang-xml prettyprint-override"><code>&lt;Table id="searchResultsTable"
                 selectionMode="MultiToggle"
                 visible="true"
                 items="{
                  path: '/ProductCollection',
                  sorter: {
                      path: 'AwdDate',
                      descending: true  
                  }
              }"&gt;
      &lt;columns&gt;
          &lt;Column minScreenWidth="Tablet" width="7%" demandPopin="false"&gt;
              &lt;FormattedText htmlText="Awd Date" /&gt;
          &lt;/Column&gt;
          &lt;Column minScreenWidth="Tablet" width="5%" demandPopin="false" hAlign="Left"&gt;
              &lt;FormattedText htmlText="CAGE" /&gt;
          &lt;/Column&gt;
          &lt;Column minScreenWidth="Tablet" hAlign="Left" demandPopin="false"&gt;
              &lt;FormattedText htmlText="Vendor" /&gt;
          &lt;/Column&gt;
          &lt;Column minScreenWidth="Tablet" width="4%" hAlign="Left" demandPopin="false"&gt;
              &lt;FormattedText htmlText="Type" /&gt;
          &lt;/Column&gt;
          &lt;Column minScreenWidth="Tablet" width="4%" hAlign="Left" demandPopin="false"&gt;
              &lt;FormattedText htmlText="PRC" /&gt;
          &lt;/Column&gt;
          &lt;Column minScreenWidth="Tablet" width="4%" hAlign="Left" demandPopin="false"&gt;
              &lt;FormattedText htmlText="EX" /&gt;
          &lt;/Column&gt;
          &lt;Column minScreenWidth="Tablet" width="6%" hAlign="Left" demandPopin="false"&gt;
              &lt;FormattedText htmlText="PPI Cost" /&gt;
          &lt;/Column&gt;
          &lt;Column minScreenWidth="Tablet" width="6%" hAlign="Left" demandPopin="false"&gt;
              &lt;FormattedText htmlText="Hist Cost" /&gt;
          &lt;/Column&gt;
          &lt;Column minScreenWidth="Tablet" width="4%" hAlign="Left" demandPopin="true"&gt;
              &lt;FormattedText htmlText="Unit" /&gt;
          &lt;/Column&gt;
          &lt;Column minScreenWidth="Tablet" width="10%" hAlign="Left" demandPopin="false"&gt;
              &lt;FormattedText htmlText="PIIN" /&gt;
          &lt;/Column&gt;
          &lt;Column minScreenWidth="Tablet" width="5%" hAlign="Left" demandPopin="false" sortProperty="Qty"&gt;
              &lt;FormattedText htmlText="Qty" /&gt;
          &lt;/Column&gt;
          &lt;Column minScreenWidth="Tablet" width="6%" hAlign="Left" demandPopin="false"&gt;
              &lt;FormattedText htmlText="Hist PPI" /&gt;
          &lt;/Column&gt;
          &lt;Column minScreenWidth="Tablet" width="6%" hAlign="Left" demandPopin="false"&gt;
              &lt;FormattedText htmlText="Curr PPI" /&gt;
          &lt;/Column&gt;
          &lt;Column minScreenWidth="Tablet" width="10%" hAlign="Left" demandPopin="false"&gt;
              &lt;FormattedText htmlText="PPI Factor" /&gt;
          &lt;/Column&gt;
      &lt;/columns&gt;
      &lt;items&gt;
          &lt;ColumnListItem&gt;
              &lt;cells&gt;
                  &lt;Text text="{AwdDate}"/&gt;
                  &lt;Text text="{CAGE}" /&gt;
                  &lt;Text text="{Vendor}" /&gt;
                  &lt;Text text="{Type}" /&gt;
                  &lt;Text text="{PRC}" /&gt;
                  &lt;Text text="{EX}" /&gt;
                  &lt;Text text="${PPICost}" /&gt;
                  &lt;Text text="${HistCost}" /&gt;
                  &lt;Text text="{Unit}" Style="font-color:red" /&gt;
                  &lt;Link        text="{PIIN}"
                          press="handleLinkPress" app:mydata="{HistPPI},{Qty},{AwdDate}" /&gt;
                  &lt;Text text="{Qty}" /&gt;
                  &lt;Text text="{HistPPI}" /&gt;
                  &lt;Text text="{CurrentPPI}" /&gt;
                  &lt;Text text="{PPIConversionFactor}" /&gt;
              &lt;/cells&gt;
          &lt;/ColumnListItem&gt;
      &lt;/items&gt;
  &lt;/Table&gt;
  </code></pre>