Add a list view to the place tracker app. (#30)

* Add list view to place tracker. Note: map in listTile is not WAI in this commit.

* Remove map from list tiles. Make list tiles tappable (currently editing a place and saving will do nothing if the details screen is pushed from the list view.

* Fix text alignment in list.

* Initial implementation of using an InheritedWidget to maintain data between list and map. Map does not update correctly at this point.

* Use AppModel.update to set the AppState. Add MapConfiguration class to handle map changes based on AppState.

* Don't cache AppState - lookup directly. Extract AppState code into it's own file and add static methods. Address comments from Hans.

* Extract generic AppModel code.

place_tracker/pubspec.yaml

@@ -17,6 +17,8 @@ dependencies:
       url: git://github.com/flutter/plugins
       path: packages/google_maps_flutter
 
+  uuid: 1.0.3
+
 dev_dependencies:
   flutter_test:
     sdk: flutter