Add $cordovaProgress.show(message) for Android

@linuxjuggler brought it to my attention that even though the base ProgressIndicator plugin had Android support, it did not exist in ngCordova.  Added the following to ngCordova:

```
$cordovaProgress.show(message)
```

The base plugin has the following craziness:

```
ProgressIndicator.show(_type, _dim, _label, _detail)
```

However, it looks like that is never used anywhere.  The Android function of that only expects a single parameter.

It is important to note that `show(message)` is for Android only.