Add initial tests for App and generator

[dekpient]

This PR adds some unit tests and user interaction tests for issue #10

I've also enabled coverage report and add a test job as part of the build workflow. Hope this helps! 😃

[dekpient]

 PASS  src/generator/__test__/index.test.js
  ✓ generating minimum policy (4ms)

 PASS  src/App.test.js (5.901s)
  ✓ display the generated policy for the given project data (2034ms)
  ✓ display error for invalid account ID (905ms)

--------------------|----------|----------|----------|----------|-------------------|
File                |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
--------------------|----------|----------|----------|----------|-------------------|
All files           |    39.82 |    38.46 |    18.18 |    39.82 |                   |
 src                |    14.29 |    11.11 |     5.56 |    14.29 |                   |
  App.js            |     87.5 |      100 |       50 |     87.5 |                81 |
  index.js          |        0 |      100 |      100 |        0 |             10,20 |
  serviceWorker.js  |        0 |        0 |        0 |        0 |... 32,133,135,138 |
 src/components     |    64.29 |    38.89 |    44.44 |    64.29 |                   |
  Form.js           |      100 |       50 |      100 |      100 |... 48,279,310,341 |
  ResourcesArray.js |     37.5 |    16.67 |    16.67 |     37.5 |    27,31,41,52,61 |
 src/generator      |       44 |       50 |     12.5 |       44 |                   |
  index.js          |       44 |       50 |     12.5 |       44 |... ,92,97,100,105 |
 src/validation     |       72 |    61.76 |      100 |       72 |                   |
  index.js          |       72 |    61.76 |      100 |       72 |... 28,32,36,40,44 |
--------------------|----------|----------|----------|----------|-------------------|
Test Suites: 2 passed, 2 total
Tests:       3 passed, 3 total
Snapshots:   0 total
Time:        8.164s, estimated 9s
Ran all test suites.

[nadunindunil]

Thank you