Check if ImageLoader is already initialized.

Didn't realise that `IntentService` is destroyed when it's work is done, unlike `Service`, so `onStart` is basically called on every notification. Simple check to `imageLoader.isInited()` and exit early if so.
hum... for the sake of maintanability, what do you think of inverting the condition?

```java
if(!imageLoader.isInited) {
 // Do init stuff
}
```

That way we avoid early return and possible problems when someone add something else to the `onCreate()`