[Android] Support permissions field for manifest.json.

1. Parse permissions from manifest.json with ApplicationData
   class.
2. Add method getPermissions for Java to get permissions of
   current app.

Bug=https://crosswalk-project.org/jira/browse/XWALK-651
[Android] Add tests for manifest.json permissions.
This tests covers 3 situations, including:
1. GetPermissions, test manifest.json with 1 permission definded.
2. GetEmptyPermission, test manifest.json with 0 permission definded.
3. GetNullPermission, test manifest.json without permission field.