chore(db-scripts): add new columns to ACT_RU_EXECUTION

This commit adds two new columns to db table "ACT_RU_EXECUTION":

* CASE_INST_ID_
* SUPER_CASE_EXEC_

Furthermore the foreign key constraint on ACT_RU_TASK.CASE_INST_ID_ has
been removed.

This commit is used as a basic for the implementation of the behavior of
the ProcessTask.

related to CAM-2371
WIP