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 ;)
Couldn't you just change this line to be backward compatible?

```java
getStringPreference(context, VIBRATE_PREF, getBooleanPreference(context, VIBRATE_PREF, true) ? "default" : "disabled");
```