MDL-6095 - Question bank tables are created by the quiz module. The really core table...

MDL-6095 - Question bank tables are created by the quiz module. The really core tables are now created by lib/db, the datasetdependent tables are not created by the datasetdependent question type, and the question_numerical_units table is now created by the numerical question type. The last two are shared by the calculated question type, but there is no problem with them being created in the order they are now created in. In the past, before the policy that upgrade to 2.0 woudl have to go via 1.9, there would have been bit problems to do with the order of updates, but fortunately that is no longer an issue.