Remove now unused parts of multiplayer code from LoW.
Add newly introduced MP campaign attributes to LoW.
Adjust mp::connect and mp::configure for debug mode.
Add default "Custom" faction for sides without recruits in LoW.

This indicates that the faction should be locked to "Custom" faction and
player would not be able to select any other faction.
Adjust mp::connect for "no_leader" SideWML attribute.
Adjust gender locking (mp::connect).

Side is now locked to a default unit's gender if no gender was provided
by WML author and "Use map settings" are on.
Adjusted playable sides for LoW.

The changes are not final:
"Costly Revenge" and "Elvish Assasins" scenario sides need specific
adjustments for MP. E.g. gold, placement.
"Elves' Last Stand" and "The Chief Must Die" have different number of
sides than other scenarios in the same chapters.

In addition, mp::connect_engine's side controller set up has been
slightly adjusted.
Further adjustment for playable sides for LoW.

Since "The Chief Must Die" is not suitable for MP at this point, because
it has too few sides, thus it will be skipped in MP.
Improved "save_id" handling for SideWML (mp::connect).
Ran wmlindent on LoW.
Ran wmllint on LoW.
Fixed config to bool explicit conversion.