Feature #4977: Implement two level of progression in AssetsManager
Feature #4977: Bug fixes for download resuming
Feature #4977: Improve log informations and event messages
Feature #4977: [AssetsManager] Implement server resuming support check
Merge branch 'v3_assets_manager' of git://github.com/cocos2d-html5/cocos2d-x into AMMerge

Conflicts:
	extensions/assets-manager/Downloader.cpp
Merge pull request #65 from pandamicro/AMMerge

Merge AssetsManager improvement