Move explanation of Akka Typed in slide deck

[eloots]

At the end of the A recap on Scala 2 - Akka Typed - Dotty chapter, about 4 slides explain an Actor's protocol and the utilisation of message wrappers and adapters.
It's better to move these to the chapter on Union Types for two reasons:

• It shortens the already quite long recap chapter
• It gives information about message adapters at the moment where this is useful for solving the exercise in the chapter on Union Types

[eloots]

Done