Add Google Maps Place Tracker sample app to flutter/samples. (#20)

Sample app that displays places on a map. Add/edit places. Interact with map. Iterations to follow.

place_tracker/ios/Runner/AppDelegate.m

@@ -0,0 +1,13 @@
+#include "AppDelegate.h"
+#include "GeneratedPluginRegistrant.h"
+
+@implementation AppDelegate
+
+- (BOOL)application:(UIApplication *)application
+    didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
+  [GeneratedPluginRegistrant registerWithRegistry:self];
+  // Override point for customization after application launch.
+  return [super application:application didFinishLaunchingWithOptions:launchOptions];
+}
+
+@end