Trains should respect signal aspects

[ashivasubramanian]

Currently, trains do not stop before a signal if the signal aspect is red or slow down if the signal aspect is amber.

This should be fixed because as per the functional spec,

Red: The train shall come to a complete stop just before the signal.
Green: The train can travel at any speed as long as it does not exceed MPS.
Amber: The train can travel at a speed that does not exceed half of the MPS.

• [ ] Convert Stations into Observables. Ensure Train has both stops & stations.
• [ ] On game load, Trains should register for the relevant upcoming Station as an observer.
• [ ] Once train crosses the station, it should deregister as an Observer for that station.
• [ ] Once train crosses the station, it should register as an Observer for the next station.
• [ ] Green aspect speeds
• [ ] Amber aspect speed strategy
• [ ] Red aspect stop strategy

[ashivasubramanian]

This is easier to debug once #11 is done. So that should be done first.