Item system v1

[noah1510]

This issue is about implementing the v1 of the item system.

The requirements for it are already in the documentation directory.

• finish the item specification
• finish the effects specification
• implement the basic item class
• implement the data registry
• load a config file into an item registry
• implement a basic shop
• implement the item effects
  • implement passive effects
  • implement active effects
• handle synchronization of the item data with the clients
  • sync the map manifest data with the clients
  • send missing data files to client when requested
• find a way to cache the item data