Add dummy interfaces for BuildDBStep
DBDefinition Written.
Added getNextPartition to DataStore
Constructor Added
Added simple build DB step and some partition set utils for inverting
Constructor Corrected.
Merge branch 'build-db-step' of https://github.com/linqs/psl into build-db-step
Standard predicate instead of predicate
Added getNextPartition to DataStore
Drafted DataSplitter and ExperimentTree.
Fixed some warnings, added documentation, new QueryAtom-based BuildDBStep
Merge branch 'build-db-step' of github.com:linqs/psl into build-db-step
Merge branch 'build-db-step' into closure-step
Added some imports.