Pick fixes from next (cocos#3024)

* fix editbox show multi labels when editing (cocos#3015)

* fix load ttf with md5 (cocos#3016)

Fix beta user reported issues in Label & Spine (cocos#3008)

* Fix label dark border issue

* Secure Skeleton listener setting

fix the loadResDir function param transfer problem (cocos#2992)

fix loadResDir completeCallback absent issue

Merge branch 'v1.9'

Merge branch 'v1.9-release'

update version to 1.6.0