Put more stuff in WelcomeMessage #43
Description
Currently the messages are too fragmented. Stuff that will only be sent once when the server connects to clients (such as PlaybackSessionListMessage) should be included in the welcome message (as that is the whole point of a welcome message).
This change would not only make the code easier to understand as the client would not be waiting for a random message to get sent to do a task, but also reduce chances of undefined behavior when connecting to an unofficial client or server.