Expose DatabaseAdapter to simplify application tests (#1121)

* Move helper.clearData to DatabaseAdapter. Expose DatabaseAdapter in index

* fix indentation

* Export DatabaseAdapter in index.js

* Rename clearData to destroyAllDataPermanently. Only export destroyAllDataPermanently from DatabaseAdapter. Update helper

* Expose wrapped TestUtils from index.js. TestUtils exposed select functions from other modules, only in test environment

src/TestUtils.js

@@ -0,0 +1,15 @@
+import { destroyAllDataPermanently } from './DatabaseAdapter';
+
+let unsupported = function() {
+  throw 'Only supported in test environment';
+};
+
+let _destroyAllDataPermanently;
+if (process.env.TESTING) {
+  _destroyAllDataPermanently = destroyAllDataPermanently;
+} else {
+  _destroyAllDataPermanently = unsupported;
+}
+
+export default {
+    destroyAllDataPermanently: _destroyAllDataPermanently};