To fix all possible situations when active message box overlaps with loading
screen progress.
The only used condition to center loading screen progress by height is
number of message boxes > 0. No need to pass it through interface.
LoadingScreen can check it inside setLabel function.
The progress is not particularly accurate. It simply uses the current / total number of records written/read as indication. Cell records are currently the largest by far, but there is a good chance that could be optimized using a change tracking system.