Allow multiple CCLA invitations to be sent at once

:fork_and_knife: You may now specify a comma separated list of email addresses to invite contributors to a CCLA.
Fixed it as part of: https://github.com/opscode/supermarket/pull/500

A feature spec for the Contribute sections of the app would have caught this, which was an oversight on my end. I will be sure to write feature specs for those parts of the app in the coming days.