Collapsed comment is not focusable from the keyboard

[TomaszGasior]

In e3fc390 collapsed comment has been implemented. By default content of comment column in the radio list is placed directly in table cell. When this feature is enabled manually by the user, comment content is replaced by small icon and text is available by tooltip.

While this kind of implementation is accessible for users with mouse and for users with screen reader, users with keyboard only are not able to access contents of collapsed column. Current implementation uses HTML title attribute, built-in tooltip provided by web browsers. It seems to me that the only way to make collapsed comment accessible for keyboard-only users is to use proper JavaScript implementation of tooltip.

#15