Add CommonKit and Activity

[Anderas]

Relates to #4829

Create a new local CommonKit framework that contains Activity and ActivityCenter, to be used by a future PR to display activity indicators, info and error messages. The idea behind an activity is that it encapsulates the state of some temporary UI, and may be added to a queue of multiple activities, only showing one at a time.

CommonKit is a separate framework, so it is easier and faster to build and run tests against, thus making it easier to do TDD. In the future the framework may be extracted to a separate repo if used by other clients / projects

[github-actions]

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[stefanceriu]

Great! 👏