[Android] Fix the build issue caused by different Android OS Version.

Since different Android APIs are imported in different Android OS version,
the OS version with lower API level uses the API in high API level, which
causes issue. This fix resolves the issue by adding the control condition
in the API uses of different API levels.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1081
Merge pull request #1657 from ShDavidliu/APILevel

[Android] Fix the build issue caused by different Android OS Version.
[Android] Split crosswalk into core layer and runtime layer.

Originally the two layers are compiled into one Java package. It needs to
split them into two different directories for building because core will
be published as an Android library without runtime layer code.
Besides that, there are also 2 major changes:
1. Move Java extension mechanism and extensions inside core layer.
2. Change the 'runtimelib' to 'runtime_lib'.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1041
Merge pull request #1649 from yongsheng/fix1041

[Android] Build crosswalk into core layer and runtime layer respectively...
[Android] Change targetSdkVersion from 17 to 19 for AndroidManifest.xml.

AndroidManifest.xml of all Android projects should be changed to build
with Android 19 API and SDK.
Fix multiple crashes of xwalk_browsertest in Debug mode

Runtime is responsible for creating and destroying the ui::Compositor through
NativeAppWindow. So, we should call window Close() before discarding the
Runtime and we should wait for the window is actually closed so that the
compositor is deleted normally (Credits to @nagineni for the preliminary
analysis).

Another problem which is fixed by this patch is the early return from the
"XWalkBrowserMainParts::PreMainMessageLoopRun" method if application system
managed to handle command line arguments as this did not take into account
the "parameters_.ui_task". This problem led to hanging of some browser tests
that were using command line arguments e.g. "ApplicationOnInstalledEventTest".

https://crosswalk-project.org/jira/browse/XWALK-1014
Merge pull request #1655 from pozdnyakov/Fix_browser_tests_crashes

Fix multiple crashes of xwalk_browsertest in Debug mode
Modify ApplicationMultiAppTest test

Modify ApplicationMultiAppTest test so that it won't fail
when XWalk start up URL changes to "about:blank"
(https://github.com/crosswalk-project/crosswalk/pull/1577).
Merge pull request #1660 from pozdnyakov/modify_ApplicationMultiAppTest

Modify ApplicationMultiAppTest test
Merge pull request #1659 from yongsheng/api19

[Android] Change targetSdkVersion from 17 to 19 for AndroidManifest.xml.
[Android] Allow extension manager to load extension js from res/raw

This is step one of getting rid of assets for xwalk_core_library.
Because assets are not supported well for android library project.

Now XWalkExtensionManager will load extension js files from res/raw
first for internal extensions, then from assets if not found.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1084