title: p:datatable rows by default editable
body: <p>so i have p:commpandButton which loads p:datatable on ajax see picture One.
  I want p:datatable in editable mode by default (when it loads) see picture two</p>
  
  <p><strong>picture One:</strong> 
  <img src="https://i.stack.imgur.com/VZr6q.png" alt="enter image description here"></p>
  
  <p><strong>picture Two:</strong> 
   <img src="https://i.stack.imgur.com/HWSB9.png" alt="enter image description here"></p>
  
  <p>here is p:datatable :</p>
  
  <pre><code>&lt;ui:composition template="/template/mastertemplate.xhtml"&gt;
    &lt;ui:define name="content"&gt;
      &lt;h:form styleClass="form" prependId="false"&gt;
        &lt;p:panel id="analysisTheBudgetPenel" header="Analysis The Budget"&gt;
          &lt;p:tabView id="scenarioTabViewId" style="width:850px"&gt;
             &lt;p:tab title="Scenario One" id="scen"&gt;
                &lt;h:selectBooleanCheckbox id="isApprovedBooleanId_checkBox" value="#{budgetAnalysisAction.budgetScenarioHescoProposalBean.abc}" /&gt;
                &lt;p:scrollPanel style="width:800px; height:auto;"&gt;
                &lt;p:dataTable id="budgetAnalysisDataTableId" rowIndexVar="index" editable="true" resizableColumns="true" value="#{budgetAnalysisAction.budgetScenarioHescoProposalBean.budgetScenarioHescoProposalListBean}" var="budgetScenarioHescoProposalList"&gt;
                   &lt;p:ajax event="rowEdit" process="#{scenarioTabViewId:isApprovedBooleanId_checkBox}" listener="#{budgetAnalysisAction.testAjax}" /&gt;
  // some columns
  // closing tags of above
  </code></pre>