ENYO-3914: Hide play image overlay when programmatically played, general cleanup.

Issue
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The sample was not hiding the play image overlay when the video was played via the play button located beneath the video.

Fix
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General cleanup and better state management (via bindings) to hide/show play image overlay.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>