Add new regression tests

Refactor PageAnnotationImportSystemTest

- Rename PageWithTemplateInclusionRegressionTest
- Add DatePropertyRegressionTest
- Add MwImporter to handle only the imported tasks
- Add MwImporterTestBase which encapsulate import and
setup tasks
Preliminary adoption of SQLite/SMWSQLStore3Query to make tests work

This is necessary to make sure that regression/integration tests run on
SQLite as well otherwise you get whole lot of errors.
Some tidy work
More clean-up

Split methods from MwImporterTestBase and
- Move asserts into SemanticDataAsserts
- Move data fetching into SemanticDataFetcher
- Add valueFormatter callback for assertThatPropertyValueIsSet
Improve readability