Set up javascript, vue and UI testing

[MrNaif2018]

Currently we only run eslint linting by yarn lint:
https://github.com/bitcartcc/bitcart-admin/blob/6a3e10391ef22dead01e0b9a65a2dba393ccdc4c/package.json#L12
To get to 1.0 release, we need a stable test suite to test that UI doesn't break without checking it manually (for example when upgrading one image input library it got broken and got into release, so I had to fix it later manually)
I am not an expert in javascript apps (and vue apps) testing, so any help welcome
We need a few categories of tests set up:

1. Unit tests. I heard that jest is often used for this. We may test some utility functions and so on. For code coverage codecov is to be used of course.
2. Integration tests: something that may be tested on a real API. This could either use our demo merchants api instance (https://api.bitcartcc.com), or better, it would start the most recent changes from bitcart master repo in docker
3. End to end tests and snapshot testing. This type of testing is the most important one. Something like selenium could be used, or better-suiting libraries for that in js world. It would test that UI works as expected.
   This would then be added to our CI. If you need help in adding it, you can just implement the tests and I can add that to CI.
   First of all we need to scaffold the initial infrastructure for that, then add those test types and start adding new tests. This issue can yield a lot of pull requests because there are a lot of tests to add or set up.