{{action}} and {{linkTo}} now default to bubbles=false (stopPropagation)

/cc @devinus re 62d6c7220e55987127b19e6136b75e55a3e4a5d7

I claim that *not* bubbling is the most common use case for action handlers, in particular having links/buttons inside a clickable area, like on Twitter:

![Screenshot 1:21:13 15:27-2](https://f.cloud.github.com/assets/524783/83234/c1c62f7a-63d6-11e2-8e61-fc16c5a34e4a.png)

Let's make it the default.

`old-router` still bubbles by default; it doesn't even have a `bubbles` option. I'm leaving it unchanged for simplicity and compatibility.