Reversing #177 & additional tests

[manueltimita]

Reversing #177. Implemented additional tests to try and catch the reported behaviour (see discussion).

What

It was reported that changed is not properly triggered in subscription when an array property in a child publication is being updated. Tests were added to validate whether this is indeed the case. The results so far point to changed being triggered without problems under the reported circumstances.

Additionally:

• All tests have been modified to only use the sync minimongo API, for simplicity (e.g. use Collection.find().fetch().length instead of Collection.countDocuments()).
• README updated with instructions for testing.

Why

PR #177 proposes a change which may lead to unexpected behaviour. The new tests show that either with, or without this change, the updates are propagated without any visible issues. If the problem persists, the test suite should be expanded with the exact case that reproduces the issue.

[StorytellerCZ]

Will be released in v1.8.8