Graceful error handling

[jeroen]

Right now, the player crashes and throws undecipherable error messages to the API when something is wrong. We should:

• move the player back to an idle state
• generate a user-friendly error message
• show that error message in the display.

As an example, the most common error is probably the file not found. It can be easily faked by setting a nonexisting video. This throws the following error in Safari:

• INVALID_STATE_ERR: DOM Exception 11.

We probably want it to say something like:

• File not found: /static/video/bunnu.mp4

This error translation logic should probably live at the Model / View level, so both internal components and external (API) scripts can leverage them.