Add notify type preference.

WIP: still testing to make sure this works as expected

![image](https://cloud.githubusercontent.com/assets/4513759/4461747/f6cedbd2-48bc-11e4-8a20-39533c57a5e6.png)

This adds a preference to not receive all messages, and only mentions/1-1 messages (like the official app) or maybe just 1-1 messages.

Depends on https://github.com/Neamar/notiflow-server/pull/7
small trouble: on the next message, the priority will change again to standard. Maybe we should keep the priority value?