Updated ZSContextWatcher, ZSReachability, added shared header.

Made it so context watcher can fire notifications only if a given context matches the saving context. It still supports watching a persistent store coordinator Context watcher seems like it was supposed to send the results with the notification. I changed it so it does because the results were needed in my code. Changed ZSReachability define name to not conflict with other code. Added shared header so the code compiles on its own.

I changed the init method names because the initWithMOC method now has different functionality. I would rather have an existing user of this code have their code fail to compile so they look into what changed.