Refactor Processor Integration Tests

The existing integration tests for 'processors' share a common set of test cases, but since this is not enforced there are processors that are missing tests.  This code is an attempt to resolve this by creating base test classes, similar to the generator unit test base classes, refactoring existing test code and adding extra test where necessary.

### Scope
Whilst these changes do affect all the existing processors, the main focus of this work is to improve the following processors:

* Firebird
* Oracle
* Postgres
* SqlServer
* SqlServerCe

The reason for not including Jet, MySql and SQLite was that there was so little integration test coverage for tables, columns, etc.  The hope is that this code will help others in the future improve the test coverage of those processors.

### Notes
It is worth noting that these changes have been tested with each RDMS and I have not found that any of these test fail.  Please let me know if the integration tests no longer passing for you.