Custom changeset fixes

- ChangeSetDelegate.customchange : use change.setClasss instead of direct assignment, the setter instantiate the custom change class.

- CustomProgrammaticChangeWrapper : remove this redundant class 
this class was missing  annotation which is required by liquibase infra, and also missing some implementation which is needed for check-sum generation.

- Align custom task and custom pre condition to use same parameter className(without breaking the api). I found it confusing and even in this repo there was a mistake.

Thx, Avihay