Add unit test to check boolean conversion with and without PDO boolean type

Add functional test to check null conversion with boolean type. This test required NULL to be allowed in the table column.

TimeType resets date fields (i.e. unused DateTime object fields) to UNIX
epoch (1970-01-01). This makes TIME field mapping stabe (i.e. same time
will be always mapped to the same DateTime fields).

See DDC-179 (similar issue with DateType). Fixes DBAL-993.