MEDFORD, Mass. — Colleges are paying students to take a year off after high school to travel, volunteer or do internships so that students of all income brackets can benefit from “gap years.” A new program at Tufts University and existing ones at a handful of other schools aim to remove the financial barriers that can keep cash-strapped students from exploring different communities and challenge their comfort zones before jumping right into college. The gap year program starting this fall at Tufts will pay for housing, airfare and even visa fees, which can often add up to $30,000 or more....