LDEV-3962 Similar changes done to Open Lesson dialog as previously done to Open/Save sequence in authoring
* ability to save sequences on pressing the Enter button when title input is focused
* focus title input field in case this element is visible in the current viewport (to avoid unwanted scrolling)
* ability to start lessons on double click
* prevent sequences from being deselected on any subsequent clicks
* Make 'Tour' word to appear after icon in order to be consistent with the rest of the buttons
* Make #notificationsPendingCount to be less prominent in case there are no messages. And assign it 'btn-primary' class when there are some messages available
