columnPrefix must support string and boolean, so changing to mixed
Test are for fix of ticket DDC-3028

Added 3 tests that check regression for:
- columnPrefix is empty
- columnPrefix is a string
- columnPrefix is false

Added some small entity / embeddable classes to support the test cases.
This fixes ticket DDC-3028

Enables columnPrefix to be "false" so no prefix is added.
Changed the structure a bit (to if/else) to be more readable with the additional condition.