[Android] Launch Screen 2nd-step implementation

This is the second step implementation of Launch Screen feature.
As the spec defined, the launch screen contains 3 layers:
1. background color
2. background image
3. foreground image
It's impossible to show all these layers together when user tap on the icon,
because of the limitation of Android drawable, and the actual flow will be as below:
Display the first 2 background layers, and then display the 3rd foreground image layer.

Below is the description for the implementation in general:
Build scrip:
1. Parse manifest.json and customize launch screen
2. Generate drawable:launchscreen_bg.xml as the configuration defined.
3. Copy background and foreground images to res folders as expected.
Runtime:
1. Create a new layout to display 9-piece format foreground image.
2. Parse image-border from manifest.json, and customize the layout.

TODO:
One feature missed in this patch:
'ready_when' = 'user-interactive', This feature is currently under investigation,
and need to hook from content side, will support this in another patch.

Spec: https://docs.google.com/a/intel.com/document/d/17PuNuHRTQuREUpaCvj-eEx7uYi2avd-VW-oaMXMpvwo/edit?pli=1#
Bug: XWALK-637