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

### Fuseki-run
- Before: Tests: 2030, Assertions: 6051, Failures: 4, Skipped: 54
- After Tests: 2034, Assertions: 6435, Failures: 1, Skipped: 6

Relates to #340, #337