Update tests

[piotrpospiech]

It is created as a draft because there is an issue with testing package with NPM dependencies. I created the harness app to run for now only react-meteor-data package tests.

Previously, api.mainModule('tests.js'); was used to add tests. However, this error occurs when it is run this way with the new Meteor version:

It can be fixed by using Npm.depends, but it cannot be made only for tests.

If the client and server code will be stored in different files, then adding tests as I made here api.addFiles(['useFind.ts', 'useFind.tests.js'], 'client'); will be available. However, we will need to rewrite those packages completely.

Is there any way to split client and server code because the previous approach doesn't work? Now running a test on the server will throw that error.

[piotrpospiech]

1. Can we remove the react-meteor-data-harness and react-template-helper-harness then?

I kept them because I cannot migrate other tests due to the npm dependencies issue. I will remove them later.