Rename skeleton RenderMode to AnimationCacheMode (cocos#3947)

* Rename skeleton RenderMode to AnimationCacheMode

* Rename skeleton RenderMode to AnimationCacheMode

add stay on bttom to video player (cocos#3909)

Add _maxPixelRatio setting to view

Merge branch 'v2.1-release'

compatible with open data context support webgl and canvas for 2d-tas…

…ks/issues/1044 (cocos#3778)

fix load mp3 as audioClip (cocos#3712)

Merge commit '87c6aa6aca35af60a646a8a7c1709ed386aead8b' into v2.1-rel…

…ease

# Conflicts:
#	cocos2d/core/CCNode.js
#	cocos2d/core/components/CCLabelOutline.js

 default material use phone effect;fix skinning model bug (cocos#3571)

* impl texture2d using imageasset

* texture-cube

* fix issue comment

* remove initWithElement and initWithData; fix issue comment

* define TextureUpdateOpts in gfx/texture-2d.js

* optimize some `new ImageAsset`; optimize image-asset; add updateMipmaps() to Texture2D

* use onLoaded, remove hack

* default material use phone effect;fix skinning model bug