feat: Improve Empty component again

[DiamondYuan]

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[DiamondYuan]

@zombieJ 先 review 实现吧，可以的话我再把 测试/demo 改了。

[netlify]

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[DiamondYuan]

ImageType 这个名字是否需要改成 EmptyImage

[codecov]

Codecov Report

Merging #15487 into feature will decrease coverage by 0.03%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           feature   #15487      +/-   ##
===========================================
- Coverage    94.14%    94.1%   -0.04%     
===========================================
  Files          250      250              
  Lines         6643     6637       -6     
  Branches      1931     1940       +9     
===========================================
- Hits          6254     6246       -8     
- Misses         388      390       +2     
  Partials         1        1

Impacted Files	Coverage Δ
components/config-provider/renderEmpty.tsx	86.66% <100%> (ø)	⬆️
components/empty/index.tsx	94.73% <100%> (-1.27%)	⬇️
components/upload/UploadList.tsx	94.49% <0%> (-1.84%)	⬇️

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[DiamondYuan]

用 base64 ?

@afc163

现在还是 feature 分支，图片地址改了。不方便用 GitHub 的图片

或者干脆删了这一段？反正下面的 demo 里面已经写了

[afc163]

文档里直接贴链接展示就行。

![image](https://user-images.githubusercontent.com/507615/54591670-ac0a0180-4a65-11e9-846c-e55ffce0fe7b.png)

![image](https://user-images.githubusercontent.com/507615/54591679-b0ceb580-4a65-11e9-925c-ad15b4eae93d.png)

[afc163]

#15442