Show start time or starting position on slider and VCR

**Jira Issue**

- [BLD-823](https://edx-wiki.atlassian.net/browse/BLD-823)
- [BLD-869](https://edx-wiki.atlassian.net/browse/BLD-869)

**Description**

When the start time is set, or a initial position is set,the VCR timer and the time slider should jump to correct starting point before the video starts playing.

**Solution**

When metadata is loaded for the HTML5, or YouTube video, we call the updating of VCR and the slider to show the duration o0f the video. Up to now, the initial time was set to 00:00. Now we will set the initial time to either the start-time or the saved position (depending whether the start-time is set).

**Reviewers**

- @polesye 
- @jmclaus