Revert addition of PARENTLOCKMODE_ column

In JBPM-1755, a new column PARENTLOCKMODE_ was added to table JBPM_NODE for persisting field Join.parentLockMode. Turns out the schema change is a barrier for our customers to upgrade to newer versions.

The proposed solution is to provide two different mappings for the Join class, with and without the column. The provided Hibernate configuration will include the mapping without the column by default. Interested parties may inclde the version with the column in their own Hibernate configuration.