Pause/Resume Sound on Start/Stop Timeline
Sound is cleared on playback step forward/back as would become out of sync and no easy way to SFX time seek.
Merge pull request #701 from cocojoe/v1.1

Fix #694 - Sound Effects on Timeline preview don't stop on stop button
Merge branch 'v1.1' of https://github.com/spritebuilder/SpriteBuilder into v1.1