Feature/581 en api v2

[solita-pekko]

Modified app to use version 2 of the Exposure Notifications API.

• Instead of displaying the number of exposures, the app now displays the number of days for which new exposures have been detected.
• Only exposures newer than the latest currently known exposure are handled.
• The app is now responsible for displaying local notifications about exposures.
• Minimum supported iOS version increased to 13.7 / only v2 API is supported by the app.
• App badge displays the number of 'active' potential exposures (the same number as in the app UI).

Couple of notes:

• Plural support for text ItemDaysValue could be removed as unnecessary if the final swedish version doesn't need it either (pcs).
• The local notification is removed only if the user taps it or explicitly removes it, i.e. it isn't removed when app is opened e.g. via homescreen.
• Having 2 separate implementation of ExposureNotification protocol might seem a bit excessive now that only the latest exposure date needs to be known for the v2 case too. But I wanted to keep the v1 era data objects as-is (and not add any sort of type specifying field) so kept the 2 implementations after all.

[solita-pekko]

Here is an example of how the test view > Exposure logs view looks like with the added window and scan instance information. Thought about adding a bit of text formatting like in Android, but I think it is readable enough with without any formatting. Unlike in the screenshot with generated data, the latest detection data is always added to the top of the list.