[Android] Add '--target-dir' option for packaging tool

This request comes from the Eclipse integration support.
Packaging tool will move the output APKS to the target
directory specified by developer.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1139
Merge pull request #1697 from jinbang/master

[Android] Add '--target-dir' option for packaging tool
[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'. The actual flow is 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 script:
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'

Spec=https://docs.google.com/a/intel.com/document/d/17PuNuHRTQuREUpaCvj-eEx7uYi2avd-VW-oaMXMpvwo/edit?pli=1#
BUG=XWALK-1198
[Android] Launch Screen test

Python testcase for Launch Screen feature.

BUG=XWALK-1198