Improved session timeout handling

Today's update contains changes that will improve session timeout handling in desktop browsers:

• The "Session Timeout. Please click on OK to reload the page." message typically came up after a while when the user opened and used Bookmark Ninja parallel in several browser tabs. From now in desktop browsers if page refresh is required the page will automatically reload (without showing any message) when the browser tab gets the focus.
• The "Session Timeout" message has been renamed to "Page Expired" because it describes the situation more precisely (page can expire not just because of session timeout).
• "Page Expired" ("Session Timeout") message will be still displayed when
1. the user leaves Bookmark Ninja open in a browser window for a long time (e.g. Dashboard for 12 hours) without any interaction.
2. a new build is rolled out to the server and the user has Bookmark Ninja open in their browser window.