Manager: Add System Tests

[mihai-stfc]

As a developer, I would like to have system tests for the Manager, so when making changes I can confirm nothing was broken without having to do it manually.

To-do:

1. Set up Squish (or any other appropriate testing tool) to work with the Manager.
2. Write the system tests.

Notes:

• if this is proving to take too much time, feel free to split in multiple tickets (Squish set-up, Config Entry tests, General Settings tests etc.)