Add more tests
Change implementation of reduceGraph
Work on isCenter implementation
Add test for isCenter
Add new test
Add dataset for tests
Add new data for the big dataset.
Add new tests backed by a big dataset
Use OneInstancePerTest in the code of BigGraphDecompositionSpec
Remove caching of datasets in tests.

It causes problems
Add BeforeAndAfter trait to test
Restart implementation of BallDecomposition
Add test for convertInput
Add computeBalls, sendBalls and merge functions.

Add relative tests
Add test for computeBalls
Implement computeCenters.

Also implement functions:

  - sendCardinalities
  - max
  - isCenter
  - extractBallInformation
Disable parallel execution of tests

It causes problems when using multiple SparkContexts
Add tests for computeCenters utility functions
Add tests for computeCenters
Add centers computation to main