refactor(SystemLogActions): generalize (un)subscribe handling
refactor(SystemLogActions): generalize (un)subscribe handling

Add general subsucribe and unsubscribe methods to unfity the handling
and prepare further optimaztions.

Partially closes DCOS-14431

dcos/dcos-ui,dcos/dcos-ui,dcos/dcos-ui,dcos/dcos-ui,dcos/dcos-ui