complement solution to Part 1: Warm-up of OOP Java in Lab 0.2.

Modified are the following files:

	oop_answer.md

Besides, the following 2 files are newly added:

	src/lights/Light.java
	src/lights/LightTest.java

Thank you!
							Lawrence X. Amlord
							  Apr 28th, 2014
							  Xi'an, China