fix bug chat during action

when a player chats while multiple actions from another player are
executed on the local machine we before got an assertion error becasue
replay s add_command expects that there are no other commands yet to be
processed on the replay.
(this was broken at da4cdef146bf5a1b8026f12d6b1caa6c1cd20602)
we now fix this problem by ensuring that there is never more data on the
replay than needed.

for this purpose i wrote that playturn_network_adapter.cpp whose main
purpose it to split incoming [turn]s into smaller [turn]s
we also don't need the backlog anymore because now with playturn_network_adapter we only feed process_network_data with small data pieces that can always be handled at once.

I also removed the replay_ member of turn_info.
Before, we read actions from replay_srouce and wrote actions to recorder.
And after the actions in replay_source has been executed they had been pushed into recorder.
With get_user_choice this doesn't work, because we might end up pushing the 'answer' (the user choice) of a get_user_choice in the recorder while the 'question' (the invoking user action) was in replay_source and then would be pushed onto the recorder after the 'answer', leading to a wrong order in the recorder. This could maybe also have been fixed by always pushing user choices into replay_source, and syncing the replay_source somehow after we enter a user choice, but the way it was done in this commit seemed easier.

note that replay_ and backlog were already made unused in da4cdef146bf5a1b8026f12d6b1caa6c1cd20602 (that was a rather uncomplete commit)
We maybe (i didnt test, just a guess) could also fix this bug by using add_nonundoable_command instead of add_command for nonundoable commands in replay.cpp with add_nonundoable_command  defined as:
config& add_nonundoable_command()
{
	auto c = cfg_.add_child_at("command",config(), pos_);
	pos_++;
	return c;
}
One reason why i decided against it is, that i feared add_child_at to be slow (vector::insert) if there are a lot of entries in cfg_ (for example when we join game that has already run may turns).
With the playturn_network_adapter this shouldn't be an issue anymore, but it also isnt needed anymore.
disable get_user_choice during prestart events

get_user_choice usually shows a dialog to the user. Because we shouldn't
use the screen during prestart events i disabled it there.

this commit might contain spelling corrections.
allow user_choice in prestart for invisible choices
add side parameter in sync_choice

when we call sync_choice with a third argument there was no way to
determine for which side we actualy made the decision.
fix 21905

we have one events_disabler when starting the replay_controller and a
second when entering the synced context. Thats why we have
events::commands_disabled == 1 and >1 when we are executing an action.