Export table schema (#459)

* add endpoint
* Add table-schema transformation data

app/common/WidgetOptions.ts

@@ -0,0 +1,11 @@
+import {NumberFormatOptions} from 'app/common/NumberFormat';
+
+export interface WidgetOptions extends NumberFormatOptions {
+  textColor?: 'string';
+  fillColor?: 'string';
+  alignment?: 'left' | 'center' | 'right';
+  dateFormat?: string;
+  timeFormat?: string;
+  widget?: 'HyperLink';
+  choices?: Array<string>;
+}