Add dictionary param support to resources that have AWSHelperFn props.

[LyndonHook]

Add dictionary parameter support for resources that use AWSHelperFn objects as properties. The resources can then be instantiated by using a python dictionary type instead of having to pass the actual helper function object. Its necessary if your resource creation is driven by YAML config. e.g. YAML -> Dictionary -> Troposphere Resource

[LyndonHook]

Any feedback on this? I'd love to get it merged.