TIMOB-12536: Fixes splash screen images.

Switch to using the new <splashScreens> tag in bar-descriptor.xml.
Splash images are now expected to be placed in Resources/blackberry
and the file must follow this format: splash-[w]x[h].[jpg|png].

BlackBerry will use the width (w) and height (h) to identify which image is
best for the device's current orientation.

To test create a new project and try running the app. You should see
the default splash screen (Appc logo, black background) show up instead
of the default BlackBerry image.