Update duration and remaining time displays on durationchange

[MattiasBuelens]

Description

The duration display and remaining time displays do not update when the tech dispatches a durationchange event without a timeupdate event. This PR ensures that these displays bind to durationchange to update their content.

There is a comment in DurationDisplay saying that this change should be done once a previous bug was resolved with the way player.duration() is updated on durationchange. I believe this bug was fixed with #2552, so I think it should be safe to do this change now.

Problem

In the current version, if a Tech updates its duration and only fires a durationchange event (without firing a timeupdate event), the time displays are currently not updated properly.

Steps to reproduce

1. Create a custom Tech, for example based on TechFaker
2. Set the tech's featuresTimeupdateEvents to true (to prevent the player from triggering interval-based timeupdate events)
3. Make the tech update its duration and dispatch a durationchange event
4. Notice the duration display and remaining time displays

This page demonstrates the issue when you hit the play button: http://jsbin.com/gedoxah/edit?html,output

Expected results

• The duration display and remaining time display update their content with the new duration.

Actual results

• The duration display and remaining time display are not updated with the new duration.

Specific Changes proposed

• Add durationchange listeners in DurationDisplay and RemainingTimeDisplay
• Remove the timeupdate and loadedmetadata listeners in DurationDisplay (since they are no longer needed)

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
• Reviewed by Two Core Contributors

[gkatsev]

Yeah, I think you may be right that we can just use durationchange.
LGTM.

[brandonocasey]

LGTM