pacakge-lock.json seems to be buggy now, with different OS giving different results.
See https://github.com/npm/npm/issues/17749
We have been having trouble keeping it up to date with yarn.lock. It doesn't give us a big win, because it is ignored if you install the package from npm.
This patch removes package-lock.json and starts ignoring it.
This patch introduces a goldentest.js. The tests inside
the file should rely on "golden" results rather then asserts.
For now, goldentest.js allows only image expectations. If the
actual result doesn't match the expected result, the two files
are created under `test/output` folder:
- The '-actual.png' contains the actual test result
- The '-diff.png' contains the diff between images
