Valera/bugfix tabbing video controls

This PR provides fixes for bugs:

1.) When tabbing backwards, focus should switch in succession ( https://edx-wiki.atlassian.net/browse/BLD-228 ).
2.) Tabbing from speeds to volume control doesn't close Speeds dialog ( https://edx-wiki.atlassian.net/browse/BLD-233 ).

<b>Reviewers</b>
- @polesye 
- @peter-fogg 
- @talbs Please have a quick look from the point of view of user interface. Ease of tabbing from one control to the next.