* Akka-related startup improvements

Realized that Akka Typed and Spray were not used **at all** yet there
were in the list of dependencies.
Additionally, the former would also show up in the list of Akka's
library-extensions, initialized on startup.

* Hardcode list of library extensions

Hardcoding a list of library extensions is not recommended but I don't
see any other way of disabling expensive Serialization extension, which
we don't seem to use anyway.

* fmt

* licensing update