Event verification (EXPOSUREAPP-5423) (#2524)

* Basic setup

* Test verification

* Update DefaultQRCodeVerifierTest.kt

* Invert boolean to reflect method name

* Adjustments to prepare for refactoring of "Verificationkeys" class.

* Add more tests and modify encoded event data

* Update ConfirmCheckInViewModelTest.kt

* Consider warning case

* Add test cases for warning

* Fix test

* Show error

* Add todo

* lint

* Move time warnings into result

* Update ConfirmCheckInViewModelTest.kt

Co-authored-by: Matthias Urhahn <matthias.urhahn@sap.com>