Validate animation actuators and show results in the editor UI

[ensisoft]

There's some "CanApply" functionaity that already logs warnings for actuators that can't apply at runtime.

Refactor this so that's there some "Validate" type of function in the Actuator class types and which can put the validation strings in a collection. The editor UI can then invoke the validate function on the selected actuator class and show the result in the UI.