Removes KeyframeModel from KeyframesCollection.
Improves usability of millisecond selectors of KeyframeFormViews.
Fixes bug with removing reordered keyframes.
Fixes bugs with reordered keyframes overwriting old ones.  Renames Tween tab to Motion.
Removes old duration control.
Keeps Add Keyframe button always in view.
Tweaks placement of Add Keyframe button.