DJs are about to get a cut of streaming revenue, a new source of funds for artists who typically make a living performing in front of live audiences. Mixcloud’s “Select” offering, starting at $2.99 a month per channel, represents a departure from the $10-a-month, all-you-can-eat subscriptions currently available on major music-streaming services. For the first time DJs, whose artistry involves mixing music originally created by others, can profit.