Changed ChargedPopulationInitialisationStrat to use ControlParameter.
Fix bug in SpatialCenterInitialisation

- The average position is now returned correctly.
- Added unit test for SpatialCenterInitialsation and Diversity.
Fix vector sign operation
Merge pull request #162 from robgarden/vectorSign

Fix vector sign operation
Merge pull request #157 from censlin/chargedPopRatioControlParameter

ChargedPopulationInitialisationStrat to use ControlParameter.
Merge pull request #159 from robgarden/spatialCenterFix

Fix bug in SpatialCenterInitialisation