Add lingui init command

[tricoder42]

This command installs all required packages based on project type (e.g. React vs VanillaJS). In future it should also support bootstrapping config, adding patterns to .gitignore, etc.

[codecov]

Codecov Report

Merging #253 into master will decrease coverage by 1.24%.
The diff coverage is 80%.

@@            Coverage Diff             @@
##           master     #253      +/-   ##
==========================================
- Coverage   91.86%   90.61%   -1.25%     
==========================================
  Files          38       43       +5     
  Lines         971     1002      +31     
==========================================
+ Hits          892      908      +16     
- Misses         79       94      +15

Impacted Files	Coverage Δ
packages/cli/src/lingui-init.js	78.26% <78.26%> (ø)
packages/cli/src/mocks.js	83.33% <85.71%> (-4.17%)	⬇️
packages/cli/src/api/detect.js	87.5% <0%> (-12.5%)	⬇️
packages/cli/src/api/extractors/typescript.js	91.66% <0%> (-8.34%)	⬇️
packages/cli/src/api/extract.js	97.43% <0%> (-2.57%)	⬇️
...ackages/babel-plugin-extract-messages/src/index.js	96.93% <0%> (-2.05%)	⬇️
packages/cli/src/api/formats/lingui.js	92.15% <0%> (-1.97%)	⬇️
packages/cli/src/lingui-extract.js	12.72% <0%> (-1.82%)	⬇️
packages/babel-plugin-transform-js/src/index.js	99.24% <0%> (-0.76%)	⬇️
packages/react/src/index.js	100% <0%> (ø)	⬆️
... and 6 more

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