Revise implementation of "create if has dependencies" feature

[ljacqu]

Follow-up of #31 (new issue for accurate milestones), implementation of "createIfHasDependencies" should be revised. Currently it's not so nice that it needs to be a special case within the InjectorImpl code itself. As improvement I could imagine moving the singleton store as its own handler and/or providing some sort of abort feature on the context object to stop an instantiation without any exception.