Incognito keyboard support

It'd be really useful if "incognito keyboard"[1][2] support could be enabled with a config flag like ``.

If I'm not mistaken, this would only require adding something like the following to src/android/com/ionicframework/cordova/webview/IonicWebViewEngine.java:

```
import android.support.v13.view.inputmethod.EditorInfoCompat;
import android.view.inputmethod.EditorInfo;
import android.view.inputmethod.InputConnection;

. . .

@Override
public InputConnection onCreateInputConnection(EditorInfo outAttrs) {
if (incognitoKeyboardEnabled()) {
outAttrs.imeOptions |= EditorInfoCompat.IME_FLAG_NO_PERSONALIZED_LEARNING;
}

return super.onCreateInputConnection(outAttrs);
}
```

---

1: https://www.xda-developers.com/api-apps-keyboard-incognito-mode

2: https://developer.android.com/reference/android/support/v13/view/inputmethod/EditorInfoCompat.html#IME_FLAG_NO_PERSONALIZED_LEARNING