Add plugin twitter for iOS.
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-x into develop

Conflicts:
	plugin/samples/HelloSocial/proj.ios/HelloSocial.xcodeproj/project.pbxproj
Add C++ 11 support for iOS projects.
Resolve the bug in the reflection of plugin.
Modify the license of plugin twitter.
Delete the developer ID in project config.
Merge pull request #2847 from natural-law/develop

Add twitter plugin for iOS