FlexObject::Clone issues

[drub0y]

First, FlexObject::Clone actually deserializes to a more specific subclass of StoreItem which could lead to some very strange behavior. A couple of scenarios that this would be produce unexpected results for:

• You're just cloning a "raw" FlexObject instance... why would you get back a StoreItem?
• You're cloning a subclass of StoreItem, maybe a FooItem... one would expect an instance of FooItem to come back, not just a StoreItem.

At bare minimum, the FlexObject::Clone implementation should produce an instance of the exact type that is being cloned (e.g. use this.GetType()).

Bigger picture, implementing ICloneable in .NET is generally frowned upon these days for many reasons, this being one of them. Therefore, I strongly suggest reconsidering whether the Bot Framework support any type of cloning at all. As a .NET user, I don't expect it because I am already aware of this can of worms. Guidance can always be given to those who might find a need for cloning to implement it themselves.

[cleemullins]

FlexObject is depricated in #425