Set persistent "connected" notification to minimum to drop the status icon

While having the "I'm connected!" notification is useful for many reasons (not least apparently being required to keep the app from being killed), having it actually fill status bar space with an icon is pointless and annoying. Later versions of Android let you set notification priorities precisely so that persistent "connection status" notifications can live in the notification list without taking up precious status bar space. Having read through the Android guidelines on how each priority should be used, I've set appropriate priorities for each of our notifications:

* The always-on "Connected" notification is **PRIORITY_MIN** (doesn't show in the status bar)
* The "Connecting..." notification is **PRIORITY_LOW** (shows in the status bar, but lower-than-default priority - it should only show for a few seconds, and you'll want to know that it's connecting)
* The "highlighted"/new query notification is **PRIORITY_DEFAULT** (shows in the status bar, but not as a very urgent notification; there's some argument for making it PRIORITY_HIGH, as it's used for "person-to-person" messages, but I wanted to be conservative)
* The "disconnected" notification is **PRIORITY_LOW** (shows in the status bar - you'll want to know that it's disconnected)

Things are so much tidier now :)

![screenshot_2014-11-02-19-24-08](https://cloud.githubusercontent.com/assets/1239323/4876508/d6f0925e-62c7-11e4-8bc7-d6dd1b810166.png)
![screenshot_2014-11-02-19-24-21](https://cloud.githubusercontent.com/assets/1239323/4876507/d6eef534-62c7-11e4-8fe5-ae0097cb94de.png)

(I'll re-open this as a PR for @sandsmark if you'd prefer!)