add carousel, card_swipe, and focus_image samples (#119)

* add carousel, card_swipe, and focus_image samples

* fix image assets

* fix more asset images

* add repeating animation

* fix import

* add copyright headers

* remove Center widget

* imageAssetName

* use ClipRect, refactor _SwipeableCardState

* use offset.zero

* add comments

* remove reference to coverflow package

* change spread to toList()

* refactor coverflow sample

don't set width and height
use const
data -> images

* return widget directly, fix formatting

* inline transitionsBuilder

* image -> imageAssetName

* _rectTween() => _createTween()

* _expandToPageRoute -> _createRoute

* move non-updating widgets out of AnimatedBuilder

* code review updates to animations demos

animations/lib/main.dart

@@ -3,8 +3,13 @@
 // found in the LICENSE file.
 
 import 'package:flutter/material.dart';
+
 import 'src/basics/animation_controller_demo.dart';
+import 'src/misc/card_swipe.dart';
+import 'src/misc/carousel.dart';
 import 'src/misc/expand_card.dart';
+import 'src/misc/focus_image.dart';
+import 'src/misc/repeating_animation.dart';
 
 void main() => runApp(AnimationSamples());
 
@@ -24,6 +29,11 @@ final basicDemos = [
 final miscDemos = [
   Demo('Expandable Card', ExpandCardDemo.routeName,
       (context) => ExpandCardDemo()),
+  Demo('Carousel', CarouselDemo.routeName, (context) => CarouselDemo()),
+  Demo('Focus Image', FocusImageDemo.routeName, (context) => FocusImageDemo()),
+  Demo('Card Swipe', CardSwipeDemo.routeName, (context) => CardSwipeDemo()),
+  Demo('Repeating Animation', RepeatingAnimationDemo.routeName,
+      (context) => RepeatingAnimationDemo()),
 ];
 
 final basicDemoRoutes =