Video: Refactor speed control.


Improvements:
- `construtor-prototype` is used;
- `this` refers to `SpeedControl`;
- access to `state` via `this.state`;
- fix class names (`open` -> `is-opened`, `active` -> `is-active`, etc);
- remove code duplication (`reRender`, `changeVideoSpeed`, etc);
- remove dependencies between modules;
- add docstrings;
- split complex keydown handlers and other; 
- fix `TABbing` logic;
- clean up `html`.

@jmclaus , @valera-rozuvan please review.