Integration continues...

* include/CrowdSimulation.hpp
* src/CrowdSimulation.cpp
Added field 'world', removed 'area' (it is in 'world'). Changed
constructor, so it's capable to initialize World.

* include/sim_crowd/World.hpp
* src/sim_crowd/World.cpp
Skeleton print() method.

* src/main.cpp
Changed CrowdSimulation constructor.