tests(ui): add unit testing boilerplate and first tests

[Evertvdw]

What kind of change does this PR introduce?

• Bugfix
• Feature
• Documentation
• Code style update
• Refactor
• Build-related changes
• Other, please describe: Testing!

Does this PR introduce a breaking change?

• Yes
• No

The PR fulfills these requirements:

• It's submitted to the dev branch (or v[X] branch)
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix: #xxx[,#xxx], where "xxx" is the issue number)
• It's been tested on a Cordova (iOS, Android) app
• It's been tested on a Electron app
• Any necessary documentation has been added or updated in the docs or explained in the PR's description.

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to start a new feature discussion first and wait for approval before working on it)

Other information:

[IlCallo]

Gave a first brief look and left some comments, will need to check this more in deep, but of course great work :)

[rstoenescu]

Awesome! Looking forward to merge this after comments above are resolved.

[IlCallo]

There is a weird problem with a faulty version of Cypress AE I published with the wrong name some months ago, and which apparently I'm not able to unpublish
This happens since we don't have a committed yarn.lock

@rstoenescu if you have permits, could you remove this version?
Seems like the - instead of . of all other versions is making people land on that one instead of newer beta releases

Anyway, since it was due some weeks ago, I directly released Cypress AE v4 as stable and used that one instead :)

---

I had to rebase on latest changes and adapt it to the externalization of vue and vue-router
I also added a yarn test:unit:ci for when we'll need to run it on GH pipeline
I ignored screenshots and videos folders since we don't want to commit those

Everything seems to run pretty smoothly, except a test into QSelect which is failing and the snapshots images which appear to not match anymore, as new ones are created into a different folder now.
@Evertvdw can you check out those 2 things?