Demo tamed flash in the playground (issue181107)

[jas...@gmail.com]

Reviewers: metaweta,

Description:
* Splits out the taming section of the playground
* Tamed swfobject
* Tamed alert
* Added an example on how to embed flash (without script access)
* Remember previously typed urls in the playground to ease repeated use

Please review this at http://codereview.appspot.com/181107

Affected files:
M build.xml
M src/com/google/caja/demos/playground/client/Playground.java
M src/com/google/caja/demos/playground/client/ui/Example.java
M src/com/google/caja/demos/playground/client/ui/PlaygroundView.java
A src/com/google/caja/demos/playground/taming.js