get_assert_database observations fixed

fixed bug in get_assert_database which caused
when_running_the_migrator_with_sqlserver to fail
DryRun implemented
MockDatabase renamed to decoratorBase for refactoring
DryRunDecorator refactored into separate class

To facilitate --baseline implementation MockDatabase has been splitted
into 2 and classes (basic transparent proxy and actual DryRun decorator)
Specs for baseline mode
Baseline mode has been implemented

Baseline decorator has been implemented and integrated into
DatabaseBuilder pipeline