Update AnnotationController's view model (vm) after successfully saving
a new annotation to the server for the first time.

This fixes two issues:

1. vm.annotationURI (which depends on the annotation's id, which is not
present until the save to the server succeeds) was not being set
correctly after successful save, so the annotation permalinks were not
correct until you reload them.

2. If you created a highlight while logged out, then logged in,
(AnnotationController automatically saves the highlight to the server
for you on login) the "Only Me" icon was not being shown on the
highlight until you reloaded it because vm.isPrivate wasn't set.