Add corona and dlight entities from WolfET

Made it so if cgame says a corona is visable the depth buffer is checked so don't see it through masked textures.
Made somewhat major changes in CG_Corona, AddCoronaToScene is always called. Removed CONTENTS_BOTS check to fix issue of not always seeing coronas through own bbox, because Spearmint adds local players.
I haven't tested dlight entity.