Handle incoming model values on element transition

If a value is set on the model after `pivot()` has been called, the view wasn't initialized and the animation started from 0. Now, `_start` and incomplete `_view` are initialized to the model value during the transition (no initial implicit transition).

Also remove exception handling when animating a string (color), which is faster when string are not valid colors (e.g. tooltip position). It requires to update `chartjs-color` to version 2.1.0.