[WFCORE-452] Add OperationContext.isRegisterDeployers()

Throw exception if deployers are attempted added from a subsystem
installed on the HC.
[WFCORE-452] Support for configuring/persisting subsystems in host.xml.

MODEL part only
[WFCORE-452] Support for configuring/persisting profile includes in host.xml.

MODEL part only
[WFCORE-452] Add first version of OC helper methods to determine if runtime step should run

Modify Abstract- Add-/Remove-/WriteAttribute Handlers to use the new
helper method.