Load / save login settings

- Using simple shared_preferences package for now

pubspec.lock

@@ -144,6 +144,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "2.0.2"
+  shared_preferences:
+    dependency: "direct main"
+    description:
+      name: shared_preferences
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.5.3+1"
   sky_engine:
     dependency: transitive
     description: flutter
@@ -221,3 +228,4 @@ packages:
     version: "2.1.16"
 sdks:
   dart: ">=2.2.0 <3.0.0"
+  flutter: ">=1.5.0 <2.0.0"