Added KMeans class and test

Tested test_WhenInstantiate_SetDataField
Added Kmeans class and its test
Added some tests and passed.
Merge branch 'develop' into develop_kmeans
under working on kmeans test
Merge remote-tracking branch 'origin/develop_kmeans' into develop_kmeans

Conflicts:
	src/main/java/jp/level_five/freshers/k_means/KMeans.java
	src/main/java/jp/level_five/freshers/k_means/Point2D.java
	src/test/java/jp/level_five/freshers/k_means/KMeansTest.java
Merge commit
Implemented execute() in KMeans.

For working DistanceCalculator, temporally commited.
Implemented distanceRMS method and tested
Implemented execute method and tested