Added handler to make image grayscale
Menu item added
Translation updated
History updated
Added menu option to convert color image to grayscale;
Merge branch 'feature-image-to-grayscale' into develop
Fixed signal name
Added default grayscale 4bpp preset
DialogSaveChanges replaced by QMessageBox
Updated Close Request method
Removed UI file
History updated
Icon added
Translation updated
Add saved file to recent list
Changed 'Save Changes' dialog;
Merge branch 'fix-save-dialog-1' into develop