Refactored inventory methods

Removed Inventory class >> getAndClear.
Added GameRegistry class >> clearInventory.
Switched GameRegistry instvar inventory to lazy initialization.
Removed redundant #getInventory, leaving just #inventory.
Modified "win game script" to adapt it to the changes.
Added background as instvar of Room
Added Reactor>>#getState method
Added Reactor>>#visible accessor
Extracted Door listeners installation to Door>>installListeners
Formatting
Added methods to create stand-alone Java side objects

GameRegistry>>#newJavaReactor
GameRegistry>>#newJavaRoom
Added #recreateJavaObject to Reactor and Room
Added GameRegistry>>#recreateJavaObjects

It recreates all rooms and reactors in the registry.
Added recreation of Java objects to startup.st
Formatting
Merge branch 'reinit-reactors'

Now saved images can be loaded back and used succesfully.