When app is put in background on iOS, watchPosition does not resume when app is brought to foreground.

# Bug Report
As the title explains, on iOS if your app has watchPosition enabled and tracking user movement and the user puts your app in the background, later when the app comes back to the foreground watchPosition does not resume. It does auto-resume on Android.

### What is expected to happen?
On iOS, for watchPosition to resume tracking the users position when app is restored to foreground.

### What does actually happen?
watchPosition fails to reactivate

## Information

On Android, wathcPosition automatically restarts. But for iOS I had to add this code in my device.ready() :

```
document.addEventListener("resume", onResume, false);

function onResume() {
// Handle the resume event
if (ionic.Platform.isIOS()) {
// gpsInfo.gpsEnbaled = user had already enabled GPS
// gpsInfo.gpsTrackingEnabled = watchPosition() had already been initiated
// gpsInfo.watchID = current instance of active watchPosition()

if (gpsInfo.gpsEnabled == true && gpsInfo.gpsTrackingEnabled == true) {

// if a previous watchID still exists, then kill it.
if (gpsInfo.watchID != null) {
gpsPositionTracking(0) ; // kill existing watchID if exists
}

// restart watchPosition()
gpsPositionTracking(1) ; // restart positionTracking
}
}
}
```

Start by reproducing the watchPosition lifecycle on iOS, using the foreground/background transition described in the issue and comparing it with Android behavior. Trace the iOS implementation reached by watchPosition and verify the result by confirming that an existing position watch resumes tracking after the app returns to the foreground.

Written by the indexing model from the issue text.