VWR-22690 FIXED Implemented save/load of bottomtray button order.

- Added methods responsible for saving and loading order of buttons to bottomtray. Order is saved after each drag'n'drop to
ensure user's customization of bottomtray is not lost because of crash.

- Added additional argument to layoutstack movePanel() method which tells it to move panel to the beginning of mPanels vector
without requiring a pointer to panel before which it should be inserted.

Reviewed by Vadim Savchuk.