Added entity map for getting entities by absolute tile

Conflicts:
	CorsixTH/Lua/entities/object.lua
	CorsixTH/Lua/world.lua

Conflicts:
	CorsixTH/Lua/app.lua
	CorsixTH/Lua/world.lua
Epidemics - game logic including contagious patients and vaccinations.

Changes include:
  - Added contagious variable to all disease to determine which can be part
    of epidemics
  - Contagious patient can change the disease of a non-diagnosed patient
  - Game logic, faxes and win/lose conditions and resolution
  - Support for multiple epidemics in parallel - currently disabled for balance
  - Vaccinations - UI click behaviour and nurse dispatched humanoid actions.
  - Inspector humanoid class who visits to resolve epidemic cover up.
  - Conflict resolution between emergency and epidemic faxes
St. Peter's Level files with new epidemic variables