Valera/bugfix access to hidden controls

Fix for BLD-254: Video: no access via keyboard to controls when they are hidden.

<b>Issue</b>: When controls are visible tabbing works okay, but after hiding tabbing doesn't work and we lose access to controls via keyboard.

Controls autohide for non-YouTube sources. In YouTube mode, we don't have this functionality because we can't use an overlay to cover the entire video and catch mouse enter/leave/hover events.

<b>Solution</b>: Introduce 2 invisible-to-the-eye elements which will catch focus, and transfer it to the Video controls (trigger mousemove event - autoshow Video controls).

<b>Reviewers</b>
- @jmclaus   
- @frrrances