Fix #5310 (Editor HTML menus are broken).

Override the implementation of the jquery focus() to prevent HTML menus
(class "dropdown-toggle") grabbing the focus.

Bootstrap's dropdown implementation exlicitly calls focus() which causes
currently active CM instance to lose focus. As the result, when the
command is executed, it cannot get ahold of the current editor instance.
Merge pull request #5311 from busykai/fix-5310

Fix #5310 (Editor HTML menus are broken).