There's no efficient way to pause/resume widget animations

The implementation of UMGSequencePlayer::Play and UMGSequencePlayer::Pause are not conducive to being able to efficiently pause and resume animations.

Some problems that need to be addressed:
1. Pause should not call Finish on the template instance since that tears down the whole evaluation state (this may be required currently because UMG players are recycled - investigation needed.
2. We should either make play gracefully play without setting up the whole template instance again, or add a "Resume" method if that is not possible.

Making these changes will stop having to re-create evaluation state such as track instance bindings when the sequence needs to be resumed.

1. Create a UMG animation, hook it up to play/pause button triggers
2. Hit play, the animation should play
3. Hit pause, the animation should pause as expected and not return to its initial state

Also, stick an audio track in there, pause should stop the audio from playing.