Performance update

- FIXES - fixed bugs with tabbing in create course screen - Big peformance improvement to edit-course screen for courses with huge numbers of questions and/or slower browsers - fixed duplicate questions showing in level transfer list - Optimised rendering performance further of create course area - particularly when the tree level view is open - Reduced battery consumption in play mode and create course on mobile - Significantly improved battery consumption for mobile flashcard swipe mode, also increasing frame rate on desktop - Enabled on screen keyboard for non English -> other language learning courses