fix: Restart timeout monitor if playing when reinitialised

[mister-ben]

Description

If the player is playing while the plugin is reinitialised, the playback monitor is stopped and will not restart until a play event.

Specific Changes proposed

On (re)initialisation, start the playback monitor immediately if playing.

Requirements Checklist

• [x] Feature implemented / Bug fixed
• [ ] If necessary, more likely in a feature request than a bug fix
  • [x] Unit Tests updated or fixed
  • [ ] Docs/guides updated
• [ ] Reviewed by Two Core Contributors

[mister-ben]

Not sure why travis fails, but the same failures occur on a branch unchanged from master.

[mister-ben]

The test which triggers dispose on the player causes the dispose in afterEach() to fail on 6.

https://github.com/brightcove/videojs-errors/blob/master/test/plugin.test.js#L209