anim notify states are triggered when updating thumbnails

The issue is that FAnimationSequenceThumbnailScene::SetAnimation calls referesh bone transforms which will trigger notify states present at the midpoint of the animation (as the thumbnail code sets the position of the sequence to the midpoint and performs a zero delta update). We should disable notify sampling to prevent this

1. create a new notify state
2. have the state print something from the notify begin event
3. add the notify state to an anim sequence and make sure it spans the midpoint of the clip
4. in the content browser, mouse over the anim sequence
   1. realtime thumbnails must be enabled in the content browser settings
5. note how your notify state prints to the log