Shape Key Multi-Selection and New Shape from Selected

UI should show which one is the active one, for possible new actions like Copy Shape to Active

New Shape from Mix is a good tool but we could add some utility to it. New Shape from selected would allow us to create new shapes from existing selected shapes from our mesh, this is useful for creating shapes out of ones that are bound to drivers and so their values cannot be modified with ease to suit New Shape from Mix. This function should allow us to pick which value we want to use of each selected shape, thus making it much easier to use than New Shape from Mix.