Tidy more tests

- StoreFactoryTest
- Added MwDBaseUnitTestCase::checkIfStoreCanBeUsedOtherwiseSkipTest
- RebuildConceptCacheMaintenanceRegressionTest skip due to SMWSparqlStore::getConceptCacheStatus
- RebuildPropertyStatisticsMaintenanceRegressionTest skip due to SMWSparqlStore::getPropertyTables
- PropertyStatisticsTableTest
- Sql3StubSemanticDataTest extends \PHPUnit_Framework_TestCase