DataBinding refactor support

[kennux]

Add support for renaming fields and properties databindings bound to. Sometimes when having a ui already working you want to rename a few fields and this currently breaks the databindings completely. Add an attribute you can put on the field similar to Unity's FormerlySerializedAs (name it "FormerlyBoundToAs" maybe) that can be used to remap fields.

When remapping was detected the bindings should update automatically, also there should be a context menu on any databinding root to perform this update for all children.