Extendable Item class

[saricden]

Create an Item class that extends Image (or Sprite, if animated), and adds some extra metadata during it's instantiation. So it can have a physics body if instantiated in a Level class, but can also be used in UI (possibly drag n drop bag) w/o physics.

Metadata we're going to track per Item class:

• Sprite key and animation key (if applicable)
• Add to physics to just add (physics body || UI mode)
• Money value in whatever our mid-apocalyptic currency will be
• Meta info like name, description, etc.
• isMaterial boolean

If isMaterial: true:

• Engineering attribute & value (will design system for engineering in future issue)

[saricden]

Item class should have mode boolean: uiMode (which is to say, physics is disabled, and Item is placed wherever the UI calls for).