Calculate contact normal in constructor, get rid of Contact::contact_normal
Added Simulation class to manage simulation
Simulation controlls added (incomplete)
Assertions for Simulation::prepare and ::step)
Construct particle grid
First ParticleList implementation
Use std::shared_ptr in LinkedList<T> instead of regular pointers
Added x_min/y_min for Grid and changed to shared_ptr where a LinkedList was used
Don't build layer.cpp for now
Particle copy constructor
Use shared_ptr with LinkedList in Particle
Particle rvalue copy constructor
Remove LinkedList destructor
Replace ParticelList with a simple vector<ParticleInfo>
Build simulation/particle_list
Simulation: add_particle for rvalues, use Sim::ParticleList