TraitList, TraitDict, TraitSet don't catch notification errors

Currently all three of the new container classes dispatch notification via a simple:
```
for notifier in self.notifiers:
notifier(self, index, removed, added)
```
This means that if a single notifier fails, all subsequent notifiers will not be called. This is different from the behaviour of standard Trait notification.

Trait container notifiers should have similar behaviour to trait notifiers, and if we do not fix this may lead to subtle bugs in the new observer framework where an unrelated error in a notification may mean that observers are not hooked and unhooked correctly.