Pesto polish fixes. (#4514)
Pesto polish fixes. (#4514)

- Fix the background color and AppBar transparency on the Recipe page.
- Use a Hero animation for the recipe card.
- Draw the background image under the status bar on the recipe page.
- Added instructional text on favorites page when there are no favorites.

BUG=https://github.com/flutter/flutter/issues/4403
BUG=https://github.com/flutter/flutter/issues/4405
BUG=https://github.com/flutter/flutter/issues/4436
BUG=https://github.com/flutter/flutter/issues/4399
aghassemi/flutter,tvolkert/flutter,flutter/flutter,cbracken/flutter,Hixie/flutter,flutter/flutter,aghassemi/flutter,Hixie/flutter,Hixie/flutter,flutter/flutter,tvolkert/flutter,aghassemi/flutter,tvolkert/flutter,tvolkert/flutter,tvolkert/flutter,turnidge/flutter,cbracken/flutter,turnidge/flutter,cbracken/flutter,flutter/flutter,turnidge/flutter,tvolkert/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,cbracken/flutter,flutter/flutter,aghassemi/flutter,cbracken/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,turnidge/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter,Hixie/flutter,Hixie/flutter,cbracken/flutter,cbracken/flutter,cbracken/flutter,tvolkert/flutter,turnidge/flutter,flutter/flutter,Hixie/flutter,flutter/flutter