SPRINGFIELD — Illinois and federal officials on Monday unveiled a mobile unit that they say will add speed and efficiency to digital investigations of child pornography and exploitation at a time when young people are using the internet more than ever before.The gray van is assigned to the Internet Crimes Against Children task force, said Illinois Attorney General Kwame Raoul, whose office oversees the group and its increasing caseload. Tips about alleged exploitation received by the task force increased by 118% from …