[WIP] feat: migrate to webpack@4

[sorrycc]

Close #74
Close #8

---

CHANGELOG

• remove opts.extraResolveModules
• remove opts.extraResolveExtensions
• add opts.inlineLimit
• remove aslant check
• opts.copy support Array with string
• HARD_SOURCE 不判断是否不为 none
• more testcase
• upgrade less to 3
• use assets.json for manifest, could be configured
• remove eslint check

TODO

• fixtures/copy
• fixtures/json
• fixtures/sass
• func: manifest
• func: service-worker via workbox
• func: common
• umi-plugin-dll
• upgrade less

REF

• origin getConfig.js
• webpack@4 release note
• webpack chain doc
• RIP CommonsChunkPlugin

[coveralls]

Pull Request Test Coverage Report for Build 756

• 121 of 231 (52.38%) changed or added relevant lines in 12 files are covered.
• 25 unchanged lines in 6 files lost coverage.
• Overall coverage increased (+2.1%) to 25.75%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/af-webpack/src/getUserConfig/configs/uglifyJSOptions.js	1	2	50.0%
packages/af-webpack/src/errorOverlayMiddleware.js	0	1	0.0%
packages/af-webpack/src/patchConnection.js	0	2	0.0%
packages/umi-build-dev/src/getWebpackConfig.js	0	2	0.0%
packages/af-webpack/src/getConfig/resolveDefine.js	10	12	83.33%
packages/af-webpack/src/getConfig/dev.js	0	5	0.0%
packages/af-webpack/src/getConfig/css.js	42	49	85.71%
packages/af-webpack/src/getConfig/prod.js	10	20	50.0%
packages/af-webpack/src/getConfig/index.js	58	75	77.33%
packages/af-webpack/src/build.js	0	17	0.0%

Files with Coverage Reduction	New Missed Lines	%
packages/umi-plugin-dll/src/index.js	1	0.0%
packages/af-webpack/src/dev.js	1	0.0%
packages/umi-build-dev/src/getWebpackConfig.js	2	0.0%
packages/af-webpack/src/readRc.js	2	0.0%
packages/af-webpack/src/getUserConfig/index.js	4	30.82%
packages/umi-build-dev/src/Service.js	15	0.0%

Totals
Change from base Build 726:	2.1%
Covered Lines:	631
Relevant Lines:	2559

---

💛 - Coveralls