allow Space Platform Hubs to enable/disable sending to other platforms

[sarge945]

I'm looking to make a mod that adds a MK2 Space Platform hub which allows inter-platform transfers, as I believe having them enabled from the get go reduces some of the fun relating to building self-sufficient platforms. Factorio 2.1 heavily encourages building specialized platforms and transferring resources between them, and that's interesting too, I just wish I had to make all-in-one ships for a little while first.

I'm proposing a bool be added to SpacePlatformHubPrototype called allow_transfers_to_platforms which, if false, will hide the "transfer to other platforms" checkbox (and disable the functionality).

There's a runtime setting to toggle the value of the checkbox (LuaEntity.provides_to_other_platforms), but I want to disable the functionality entirely rather than simply unchecking the box.

While there, it might be fun to add some bools for other behavior as well, such as allow_transfers_to_planet and allow_transfers_from_planet, which if set to false will disallow sending to or receiving from planets respectively (meaning we can make platforms that can ONLY send to others or receive from others), and an allow_player_travel which if false will prevent the player transporting to the platform via a rocket.

A max_connected_cargo_bays variable might also be interesting to give different tiers of hubs maximum inventory sizes.