DDS12 — Add Listener callbacks for changes in the update mode

Summary:

The CacheListener currently supports only two call-backs to signify the start and end of an update round. However because listeners are only used in enabled update mode it is important that when the DLRL switches between the enabled and disabled update mode that the listeners are notified, as the switch between update modes does not necessarily originate from the thread that registered the listener as well, and the fact that updates are enabled or disabled is a major event that should be known by the listeners.

Proposed Resolution:

Add two methods to the CacheListener interface, one for signalling a switch to automatic update mode, and for for signalling a switch to manual update mode.

see above