[WFCORE-452] Support for configuring/persisting subsystems 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.
[WFCORE-452] Rework ModelControllerServiceInitialization to boot op.

Previously the ModelControllerServiceInitialization loading was
hardcoded as part of the boot sequence. However, in order to use JMX as
a subsystem on the HC we need access to the services started by JMX's
MCSI. Putting these earlier also does not work, since patching's MCSI
needs to read values from the model, which do not get set until the boot
time. Hence this initialization has been refactored to an extra boot
RUNTIME step which has access to the model, and is able to install the
services JMX needs on a host.
[WFCORE-452] Determine if we are a master/slave before extensions are registered
[WFCORE-452] Get jmx working as a HC subsystem

Remove the hardcoded/duplicated HC RemotingConnectionService. We can now
configure it in host.xml.
Take into account whether we are a master or slave. Only master should
be able to modify attributes and add mbeans in the domain model.