remove set unneeded difficuly

we don't store difficulcy in carryover_sides_start anymore
make wesnothd use savefile format for new games

This server changes the mp wesnothd protocoll.

multiplayer conneect now works as following:
multiplayer_create/configure creates saved_game object which is then
loaded by mp_connect and sended to the server in the usual savefile
format, this especialy imples that [side] are no longer at toplevel but
instead nested into [scenario] or [snapshot].

mp options are saved into state (the saved_game object)
(state_.mp_settings()) previously we had a sperate mp_settings object
for that now we only have one mp_setting object.

In order to make mp saves work better in sp, the expansion some of
mp_settings (those that also shoudl affect next scenarios like
experince_modifier but not turns), will be moved to
saeved_game/playcampaign later.

This also temporarily disables mp modificaltion/era events/options the
reason is, that i want to move the expansion of those to saved_game.cpp
for better compability to Sp, but if that won't work i'll just enable
them how they were.

There  are still some things to do especaiyl the server genrates saved
will be completey borken, (will fix in another commit)

Also there are other things yet untested.
make wesnothd use savefile format for new games

the serverside part