Revert "Part 1: Remove unminify plugin"

[davidsbailey]

Reverts #30831 because it broke the test build:

FAILED TESTS:
  unit tests
    Applab Exporter,
      Regression tests
        ✖ should allow screens to be switched programmatically
          PhantomJS 2.1.1 (Linux 0.0.0)
        Cannot find module '../../../build/package/js/webpack-runtime.js'
        webpackMissingModule@test/unit-tests.js:750803:199
        _callee$@test/unit-tests.js:750803:202
        tryCatch@test/unit-tests.js:115099:44
        invoke@test/unit-tests.js:115367:30
        test/unit-tests.js:115132:28
        step@test/unit-tests.js:750352:191
        test/unit-tests.js:750352:441
        Promise@test/unit-tests.js:111243:15
        test/unit-tests.js:750352:110
        test/unit-tests.js:750827:28
        run@test/unit-tests.js:111141:29
        test/unit-tests.js:111158:33
        flush@test/unit-tests.js:106856:11