Merge branch 'SIMPLEITK-525_EnableDeletionOfCommandProcessExists' into SIMPLEITK-521_AddInitialRegistrationComponents

Change-Id: I2f1eda8ed484db90f49659ae15f0358a43a763db
COMP: Update return type for PreUpdateAddCommand

This is a short term fix to get things compiling, are refactoring of
overriding these methods needs to be done.

Change-Id: Idd5e139facff7c1eee99c17851e181d42a42ac65
Merge topic 'SIMPLEITK-521_AddInitialRegistrationComponents' into next

f2abb47b COMP: Update return type for PreUpdateAddCommand
69a6f5e2 Merge branch 'SIMPLEITK-525_EnableDeletionOfCommandProcessExists' into SIMPLEITK-521_AddInitialRegistrationComponents