Implement EventHandler for pre/after/post processes

To implement pre/after/post routines on core processes is possible at this moment to extend the class and override the methods prepare/doIt/postProcess.

But that's not always possible as not all processes are exposed to plugins, and also in some cases it can be necessary that several plugins capture the same process.

So, this ticket is to improve extensibility by implementing events for:

• pre-process - after prepare, before doIt

• after-process - after doIt, before commit

• post-process - after commit