Feature #5033: refactor Widget,Layout,Button,Checkbox
Feature #5033: refactor ImageView,LoadingBar,RichText,Slider,Text,TextAtlas,TextBMFont,TextField
Feature #5033: refactor ListView,ScrollView,PageView
Fixes two WebGL errors when minified

Two WebGL-specific files were missing which cause undefined function errors when trying to access `_tmp.WebGLColor` and `_tmp.WebGLLabelTTF` when minified.
Merge pull request #1853 from NatWeiss/patch-12

Fixes two WebGL errors when minified
Merge pull request #1852 from pandamicro/develop

Fixed #5177: use `tag` to setup tag value in ccui.Widget.getChildByTag
Feature #5033: Make ccui classes extendable in H5 and JSB
Merge pull request #1855 from joshuastray/develop

Feature #5033: Make ccui classes extendable in H5 and JSB
Issue #5096: Performance Optimization of cc.Node.sortAllChildren
Merge pull request #1857 from VisualSJ/develop-5-15

Issue #5096: Performance Optimization of cc.Node.sortAllChildren
fixed fontloader's types
Merge pull request #1858 from musikov/develop

fixed fontloader's types
Issue #5214: Add checking the file and moving log text
Merge pull request #1859 from VisualSJ/develop-5-15

Issue #5214: Add checking the file and moving log text
Issue #5216: CCEventExtension is missing of build.xml
Merge pull request #1860 from VisualSJ/develop-5-16

Issue #5216: CCEventExtension is missing of build.xml
Delete .gitmodules file
Merge pull request #1862 from VisualSJ/develop-5-19

Delete .gitmodules file
Issue #5096: Performance Optimization of cc.Sprite.sortAllChildren
Merge pull request #1863 from VisualSJ/develop-5-19

Issue #5096: Performance Optimization of cc.Sprite.sortAllChildren