Keyframe drag over left/right End

[SilvanVerhoeven]

When dragging a keyframe (fast) over the left/right end of the active area, the keyframe currently sticks to the previous position.
It should move all the way to 0/1 instead.

[frcroth]

May be related / fixed in a similar way as LivelyKernel/lively.next@614ecb2

[frcroth]

Ok still hard

[frcroth]

This is caused by the isValidDrag() call, that checks if the keyframe value would be greater than 1. If that is the case, the keyframe is reset to a previous valid position. Perhaps we should discuss what good behavior would be here. If we cause this check to clamp to 0 and 1 this issue may be fixed, but the dragging behavior will change.