Create a codelabs exercise for explicit navigation + deep linking

[zsoltk]

Codelabs are at https://github.com/bumble-tech/appyx-codelabs

Topics to cover:

• https://bumble-tech.github.io/appyx/navigation/explicit-navigation/
• https://bumble-tech.github.io/appyx/navigation/deep-linking/

When done, please also add an entry to https://bumble-tech.github.io/appyx/how-to-use-appyx/codelabs/ with a gif