added front page samples to testing, plus a couple of tweaks to front page and code lab

src/tests/site/code/collections.dart

+void main() {
+  Map famousDuos = { 'Han Solo': 'Chewbacca',      // Map literal.
+                     'Bonnie': 'Clyde',
+                     'Laurel': 'Hardy' };
+  List myFriends = [ 'Seth', 'Kathy', 'Shailen' ]; // List literal.
+
+  // Create lists and maps from Iterable objects.
+  List shuffledSidekicks = new List.from(famousDuos.values)..shuffle();
+  Map mixedDuos = new Map.fromIterables(famousDuos.keys, shuffledSidekicks);
+
+  // Iteration.
+  mixedDuos.forEach((k, v) { print('$k, $v'); });
+
+  // Some lists, maps, and sets are growable.
+  Set setOfMyFriends = new Set.from(myFriends);
+  Set famousPeople = new Set.from(famousDuos.values);
+  famousPeople.addAll(famousDuos.keys);
+
+  // Rich set of functionality for collections.
+  print(famousPeople.intersection(setOfMyFriends).isEmpty);
+  print(famousPeople.union(setOfMyFriends).length);
+}