feat(cli): add basic CLI tool

[B4nan]

Adds mikro-orm npm command that allows to clear cache and work with SchemaGenerator and EntityGenerator.

First, one needs to provide cli-config.[jt]s file in the root directory that will export the ORM configuration. You can also set up list of paths where to lookup the file.

Running with TS files is also supported via ts-node, that needs to be first enabled via your package.json:

  "mikro-orm": {
    "useTsNode": true,
    "configPaths": [
      "./src/cli-config.ts",
      "./dist/cli-config.js"
    ]
  }

Closes #101

[coveralls]

Pull Request Test Coverage Report for Build 674

• 104 of 104 (100.0%) changed or added relevant lines in 7 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 667:	0.0%
Covered Lines:	3200
Relevant Lines:	3200

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💛 - Coveralls