* Added "Remember my choice" checkbox
* Center on the screen and set position in respect to the position of mainframe or settings dialog
Preferences : Added checkboxes for enable/suppress showing of the UnsavedChangeDialog
SearchImGui : close after parameter selection_is_changed_according_to_physical_printers
PhysicalPrinterDialog, SavePresetDialog : Center on the screen
1) All slicer's exceptions are now derived from Slic3r::Exception.
2) New exceptions are defined for slicing errors.
3) Exceptions are propagated to the Plater to show.
It remains to modify the slicing back-end to throw the new SlicingError
exceptions instead of std::runtime_error and to show the other exceptions
by a message dialog instead of a notification.
* Show it on the display same as an Application
* Code refactoring : All related functions moved to the SplashScreen class
* Add a possibility o hide/show splash scree in Preferences