Action.continueWith won't be executed if its in a nested update function

[NickSeagull]

Same issue as #119 , reason is that it is polymorphic and it is probably having trouble casting from Unknown to a non-top-level event.

As a workaround, one can call the update function directly, but this could result problematic if in the future we want to parallelize workflows by registering multiple events.

Perhaps we could pass an implicit function to update that acts as this continueWith?