xwalk.gyp:xwalk_runtime Split GYP

1. xwalk.gyp:xwalk_runtime
  - xwalk porting with content layer
  - AURA/Android Port related files
2. xwalk_runtime_features.gypi
  - XWalk Features files
  - Common for Existing and EFL Port

xwalk_runtime_features.gypi will be included by
xwalk.gyp:xwalk_runtime and chromium-efl.gyp
fixup! xwalk.gyp:xwalk_runtime Split GYP
Abstraction of XWalkRunner Class

- XWalkRunner as Base class
- Common methods are implemented by XWalkRunner
- Previous XWalkRunner is now XWalkRuunerImpl : public XWalkRunner
- Porting specific methods are implemented by derived classes
- Derived classes also implements below static APIs for XWalkRunner
a. scopted_ptr<XWalkRunner> XWalkRunner::Create();
 - Create derived class Object and returns casted XWalkRunner Object
b. XWalkRunner* XWalkRunner::GetInstance();
 - Returns casted XWalkRunner class Object from Derived class Object
XWalk-EFL Porting Changes

- GYP Changes:
  For adding chromium-efl dependencies, and new macro xwalk_efl
- NativeAppWindowEfl:
  To create EFL based views, create WebContext and WebView using EWK APIs
- XWalkBrowseContext:
  Non virtual methods into vitual to inherit from BrowserContextEfl
- xwalk::Application:
  To use WebContentsDelegateEfl instead of xwalk::Runtime
- xwalk_main
  To init EWK layer and NativeAppWindow
- Build error fixes
fixup! XWalk-EFL Porting Changes