Don't trigger DocumentManager.pathDeleted on document objects too soon

This effectively fixes issue #9400 byNot triggering the `DocumentManager.pathDeleted` event on document objects when `ProjectManager` calls `DocumentManager.notifyPathDeleted()` and the path has a `Document` object.

For `Document` objects , `FileSyncManager.syncOpenDocuements()` will call  `DocumentManager.notifyFileDeleted` for each `Document` object whose view needs to be destroyed and its file removed from the working set.

Prior versions of `DocumentManager.notifyFileDeleted` called `DocumentManager.closeFullEditor()` which called `removeFromWorkingSet()`; 

Now this is done in `Pane.handleFileDeleted` when the `DocumentManager.pathDeleted` event is handled.   The `DocumentManager.notifyPathDeleted` case which triggered `DocumentManager.pathDeleted` was handled by the Editor to close down Image Views.

This is safe as no other code uses this event. There are a few extensions using this event but the impact should be positive since we don't want to trigger the event until `FileSyncManager` notifies `DocumentManager` on actual deletions. For non-document objects (images) it should be OK to dispatch the event when we get it. This will be the only time we get a notification for non-document objects anyway so we *have* to do dispatch the event during `DocumentObject.notifyPathDeleted` or it won't be removed from the working set and its view closed.

Recommended Test Scenarios:

- [ ] Open a file to the working set don't change it and delete it from the file tree
- [ ] Open a file to the working set, change it and delete it from the file tree
- [ ] Open a file to the working set, don't change it and delete it from Finder/Explorer
- [ ] Open a file but don't add it to the working set and delete it from the file tree
- [ ] Open a file but don't add it to the working set and delete it from Finder/Explorer
- [ ] Open an image to the working set and delete it from the file tree
- [ ] Open an image to the working set and delete it from Finder/Explorer
- [ ] Open an image but don't add it to the working set and delete it from the file tree
- [ ] Open an image but don't add it to the working set and delete it from Finder/Explorer
Just a note for the record: this change isn't needed to fix #9400 -- it fixes a bug that already existed on master, but was spotted by Raymond while testing this PR (https://github.com/adobe/brackets/pull/9410#issuecomment-57710658) and was in related enough code to be worth fixing here too.  (And if we didn't care about fixing that issue, the change in DocumentManager could have been to just remove the `triggerHandler()` call entirely instead of wrapping an `if` around it).