Allow items to own backpacks

[GeorgH93]

Description:

Items should be able to hold backpacks. The item would store the size of the backpack as well as it's content. It should be possible to open the backpack by right-clicking while holding the item.

Implementation:

• Config option
• Item data storage
  • Size
  • Content
  • Name
• Open mechanisms
• Custom Texture (Optional)

Possible problems:

Losing the item would result in unusable entry's in the database causing unnecessary load on the db server. Also caching of the inventories of the items would be problematic (caching all of them would waste lots of memory while not caching them would increase the time they will take to open.

It probably would make sense to implement them similar to shulkerboxes (attach the content as an nbt tag to the item) to solve the aforementioned problems.