[Android] Launch Screen full spec implementation

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 an icon is tapped, because
of the limitation of 'Android drawable' mechanism.
The actual working flow is as below:
 - Display the first 2 background layers.
 - Display the 3rd foreground image layer with a Dialog.

Below is the description for the implementation in general:
Build script:
1. Parse manifest.json and customize launch screen.
2. Generate drawable:launchscreen_bg.xml depends on the configuration defined.
3. Copy background and foreground images to res folders.
Runtime:
1. Create a new layout to display 9-piece format foreground image.
2. Parse image-border from manifest.json, and customize the layout.
3. Display the 3 layers in a Dialog.

TODO:
One feature missed in this patch:
'ready_when' = 'user-interactive'

Spec=https://docs.google.com/a/intel.com/document/d/17PuNuHRTQuREUpaCvj-eEx7uYi2avd-VW-oaMXMpvwo/edit?pli=1#
BUG=XWALK-1198
Merge pull request #1632 from kurli/launchscreen-2

[Android] Launch Screen full spec implementation