Add UINavigationController

[ephemer]

Todos

• [x] Ensure there are no memory leaks (use automated tests)
• [x] Add animations
• [x] Enable hardware back button

Non-fullscreen modal presentation (for tablets and large phones). Deliberately not covered in this PR reasons of diff size and readability. See upcoming PR.

Screenshots:

Mac

Android

Please check if the PR fulfills these requirements

• [x] Self-review: I am confident this is the simplest and clearest way to achieve the expected behaviour
• [x] There are no dependencies on other PRs or I have linked dependencies through Zenhub
• [x] The commit messages are clean and understandable
• [x] Tests for the changes have been added (for bug fixes / features)
• [x] Code runs on all relevant platforms (if major change: screenshots attached)

[ephemer]

I am going to add some more screenshots with the updated android layout (including ever-present back button etc.) and a couple from android devices, then I think we're ready to go. But code-wise this should be ready to review as is.

The diff got a fair bit larger while I added the Google Material Design licence agreement since we're using their icons.