Script executed on behalf of a script debugger is not engine-internal

While fInternal-flagged script controls may be useful for debuggers to
evaluate watch expressions because they don't get shown ingame, they
also bypass all checks the engine does and as such are a nightmare in
network play.

Part of #936.
Use control packet for player control initialization

This removes some more pre-assembled C4Script code going across the
network unchecked.

Part of #936.
Use control packet for more editor mode actions

Actions changed include dropping definitions, (de-)selecting objects,
player elimination. This removes some more pre-assembled C4Script code
going across the network unchecked.

Part of #936.