Slice handling improvements.

server/api_user.go

server/console_api_explorer.go

server/console_user.go

server/core_account.go

server/core_authenticate.go

server/core_friend.go

server/core_group.go

server/core_notification.go

server/core_storage.go

server/core_user.go

server/core_wallet.go

server/leaderboard_cache.go

server/leaderboard_rank_cache.go

server/leaderboard_scheduler.go

server/match_handler.go

server/match_presence.go

server/message_router.go

server/party_handler.go

server/runtime.go

server/runtime_go_match_core.go