* Use variableValueSource for computing variable summaries
* Rollback single <context:component-scan base-package="org.obiba.opal"/> instead of one by module
NullDatasourceFactory added.
Add @Nonnull
Fix PMD & Findbugs warnings
Fix OPAL-1748: Memory leak when importing large value sets from remote Opal
Fix OPAL-1730: Improve performance of incremental view
Remove logger
Fix warnings
Fix OPAL-1757: Drop table is slow even for empty tables