add settings and recommended extensions for vs code

.vscode/extensions.json

@@ -0,0 +1,8 @@
+{
+  "recommendations": [
+    "ms-vscode.vscode-typescript-tslint-plugin",
+    "esbenp.prettier-vscode",
+    "bierner.lit-html",
+    "bashmish.es6-string-css"
+  ]
+}

.vscode/settings.json

@@ -0,0 +1,4 @@
+{
+  "editor.formatOnSave": true,
+  "editor.defaultFormatter": "esbenp.prettier-vscode"
+}