new passphrase prompt activity

sets the stage for #1234

Gingerbread:
![gb-emu](https://cloud.githubusercontent.com/assets/373823/2966788/6f7535e6-db1b-11e3-9df8-2406caab3799.png)

JB:
![jb-ss](https://cloud.githubusercontent.com/assets/373823/2966790/72c5c49a-db1b-11e3-9a86-8fea5f5af8f0.png)