Support unread count badge in Nova Launcher + Widgetlocker (using TeslaUnread API)

This pull request adds support for updating the "unread badge" in Tesla apps (Nova Launcher Prime and WidgetLocker) using the [TeslaUnreadAPI](http://novalauncher.com/teslaunread-api/).

I really like seeing the number of unread messages next to my icons. I'm just a user, I have no affiliation with TeslaCoil Software.

Here's what it looks like (Nova Launcher Prime):
![image](https://cloud.githubusercontent.com/assets/783973/4426361/8744182a-45b2-11e4-92e8-c20d38d02eaf.png)


I've added an option to enable/disable this feature for the paranoid people (and it's off by default), but I don't mind if that doesn't get merged (to avoid adding "yet another option"); all the option-related code is isolated in the 2nd commit.

Judging by what it says on the  [TeslaUnreadAPI](http://novalauncher.com/teslaunread-api/) page about the security of the unread notification count update, it sounds like this API is more secure than broadcast-based alternatives, so maybe it's acceptable to just issue the notification in case the [TeslaUnread app](https://play.google.com/store/apps/details?id=com.teslacoilsw.notifier&hl=en_GB) is there.