fixed typo and issue of not being able to add fields in table transformation

public/app/plugins/panel/table/module.ts

@@ -94,6 +94,7 @@ class TablePanelCtrl extends MetricsPanelCtrl {
   onDataReceived(dataList) {
     this.dataRaw = dataList;
     this.pageIndex = 0;
+    this.panel.columns = [];
 
     // automatically correct transform mode based on data
     if (this.dataRaw && this.dataRaw.length) {

public/app/plugins/panel/table/transformers.ts

@@ -142,7 +142,7 @@ transformers['table'] = {
     if (!data || data.length === 0) {
       return [];
     }
-    return data[0]
+    return data[0].columns;
   },
   transform: function(data, panel, model) {
     if (!data || data.length === 0) {