Add Custom Vibrate Patterns to Settings

I added the ability to choose custom vibrate Patterns. This fixes issue #230 You can chose between:

* default
* 2x short
* 2x long
* 3x short
* 3x long
* custom (you can specify off-time, on-time)

Of course I'm open to different standard vibrate patters or other changes.

This is my first pull request and I'm quite new to Java and Android, so please be gentle ;)
yes, I thought of a check there too, but I thought its more clean when we don't check every time a notification arrives, and just once during update. But perhaps you're right and this is easier...