read-only inventories

[JackCrumpLeys]

Describe the problem related to your feature request.

Creating a Item menu I noticed that there was no obvious way to disable parts of the inventory system to do with adding and removing items.

What solution would you like?

A flag for inventory to label them as read only to the internal systems to make it so that the menu cannot be modified by anything other than the server. This could be a component or a field in Inventory.

What alternative(s) have you considered?

Re implement all the systems manually for my server, this would be non-ideal.

[dyc3]

Related to #307

[pepperoni21]

Ideally there would be an external plugin allowing to make interactive GUIs, which would be possible if we can cancel inventory click events, so this issue could be a starting point #399