Make it configurable if a deamon module is for the cms or site

When having a separate deploy of the CMS and site the site node also tries to start all daemon modules (located in: /hippo:configuration/hippo:modules).

Some daemon modules are not able to start on the site nodes because dependencies are missing. Adding the dependencies to the site module would be an option but the modules are not needed in the site node, e.g. CMS diagnostics. It would be a nice improvement if this could made configurable so we don't have the errors in the log.

Some Hippo modules that faces this problem (from the log files during the tomcat startup):
Apr 18 14:05:40 2016-04-18 14:05:40,870 ERROR [localhost-startStop-1] org.onehippo.repository.modules.ModuleManager - Cannot register module webfiles of class org.onehippo.cms7.services.webfiles.WebFilesServiceModule: class not found
Apr 18 14:05:40 2016-04-18 14:05:40,874 ERROR [localhost-startStop-1] org.onehippo.repository.modules.ModuleManager - Cannot register module diagnostics of class org.hippoecm.frontend.diagnosis.DiagnosticsDaemonModule: class not found
Apr 18 14:05:40 2016-04-18 14:05:40,875 ERROR [localhost-startStop-1] org.onehippo.repository.modules.ModuleManager - Cannot register module embargo-workflow-events-processing-module.xml of class org.onehippo.forge.embargo.repository.modules.EmbargoWorkflowEventsProcessingModule: class not found