feat: playUserInteraction & pauseUserInteraction

[Akryum]

Added two new properties to MediaElementPlayer (with docs):

• playUserInteraction: Returns whether the last play call was initiated from user interaction
• pauseUserInteraction: Returns whether the last pause call was initiated from user interaction

Example usage (for example to synchronize video events over Websockets):

mediaElement.addEventListener('play', () => {
  if (player.playUserInteraction) {
    // Example: Send event to Websocket
  }
})

mediaElement.addEventListener('pause', () => {
  const userInteraction = this.player.pauseUserInteraction &&
      // Handle when video is ended (dispatches a `pause` event)
      this.player.currentTime < this.player.duration
  if (userInteraction) {
    // Example: Send event to Websocket
  }
})

[coveralls]

Coverage remained the same at 74.376% when pulling a86a038 on Akryum:feat-play-pause-interaction into b9e74bd on mediaelement:master.

[karawitan]

LGTM

[VincentGarreau]

It could be great to merge it :)