Create Action State Cache

[thomthom]

Original report by me.

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In order to be able to correct actions via the VCB a system should be implemented that takes care of storing the info needed to recreate last action with the new input.

[thomthom]

Not implemented. Instead a more flexible EntityCache class was introduced in e5476fb.

[thomthom]

#!ruby

action = Action.new( name, surface ) { |value|
  # Generate a transformation object from given value.
  # Or perform an operation?
}
action.adjust( new_value ) # Undo, redo operation