make "player_id" the controlling client's id for ai sides.

the main intention is to simplify the serversided contoller tweaks.
simplify serversided controller tweaks

we also simplify the code by using [side]player_id= which is always the controlling client id so we don't have to distinguish between "ai", "human" and "network"

the client never sends controller="network_ai" becasue the mp connect engine converts all "network_ai" into "ai". But the serversided controller tweaks convert "ai" into "network_ai".
fix leader names in mp

"name" is here the name of the leader, previously the flg manager set it
to the name of the faction.
remove unneeded check

"save_id" isn't used to detemine which clients controlls which side. So
this check doesnt make sense.
fix segfault in [replace_map]

a default constructed vconfig was previously unable to be derefereced,
Now it can be dereferenced.
The previous behaviour led to segfaults on wrong parameters to
[replace_map].
fix [side]controller= in mp_connect

this was broken in the commit "make "player_id" the controlling client's
id for ai sides"
"Anonymous local player" -> "Anonymous player"

this string is displayed by non hosts too, so "local" is not true since
it's not local from the other clients point of view.
Also the previous string was too large for a unit name in the sidebar.
Note that this does not effect the "Local player" string in the hosts mp
connect controller options.
fixup user_description generation
fix value of "current_player" in mp_connect