[Android] Fix the issue of '--app-root' and '--app-local-path'

For make_apk.py, if the option '--app-root' is required, it's
necessary to include the option '--app-local-path' as well.
Besides, split the test cases in 'testEntry' into 2 categories:
one is for testing correct cases and another is for failures.
[Android] Implement mixed resources to fix resource not found

In shared mode, runtime client and library are in different packages.
It makes it easy to meet resource-not-found issue.

To fix that, class XWalkMixedResources is created to combine the two
resources into one. It will try to get resource from library first
and get from client when resource not found in library.

BUG=https://github.com/crosswalk-project/crosswalk/issues/796
[Android] Remove unused application customization

It's not necessary to override android.app.Application but
do nothing customized.
Remove them and just use android.app.Application in their
AndroidManifest.xml.
Merge pull request #803 from wang16/mix_resources

[Android] Implement mixed resources to fix resource not found
Merge pull request #730 from wang16/remove_app

[Android] Remove unused application customization
Merge pull request #797 from yongsheng/testentry

[Android] Fix the issue of '--app-root' and '--app-local-path'
[Android] Integrate external extensions in make_apk.py

The API for external extensions are basically ready so this is to
enable the packaging tool to package external extensions into web
app APKs.

To add one extension to be packged, developers need to do below steps:
1. Create a directory named 'foobar' and add 3 files called 'foobar.jar'
'foobar.js' and 'foobar.json' into the directory.
2. Package it when running make_apk.py:
   python make_apk.py --extensions="/path/to/foobar"

BUG=#558
Merge pull request #798 from yongsheng/extension_maker

[Android] Integrate external extensions in make_apk.py
[Android] Add the instrumentation test for runtime client.

This instrumentation test contains the embedded and shared client.
For embedded client test:
  1. install XWalkRuntimeClientEmbeddedShell.apk
  2. build/android/run_instrumentation_tests.py \
     --test-apk XWalkRuntimeClientEmbeddedTest --verbose -I

For shared client test:
  1. install XWalkRuntimeLib.apk
  2. install XWalkRuntimeClientShell.apk
  3. build/android/run_instrumentation_tests.py \
     --test-apk XWalkRuntimeClientTest --verbose -I