Extend notifications with pages on Android Wear

First iteration - adding pages to wear notifications. Also did a slight bit of refactoring, just so I could understand what was going on.

Since you don't have a watch, this is what it looks like:
![image](https://cloud.githubusercontent.com/assets/4513759/4400338/5f2c34a0-447f-11e4-8f73-8306d002a0d5.png)

So that's the default notification that you've already been sending out. Nothing's changed there. Notice how the last message there cuts off, which is because of the `InboxStyle`.

That's where the second wear-only page comes in:

![image](https://cloud.githubusercontent.com/assets/4513759/4400350/88463cc8-447f-11e4-8595-4ad66200baca.png)

This also shows all pending messages, not only the last 5. Hangouts does a similar thing, where the second page will show the whole conversation, and you can keep scrolling to see even further back (not just pending). Although I don't think Hangouts is using `BigTextStyle` like I used, since the page starts at the bottom instead of top. Maybe I'll end up creating a custom layout to fix that later.