Track CLAs signatures in SilverStripe Database

Generally, we're rethinking the Members table as it has grown to encompass more than just OpenStack Members. We now have all kinds of exceptions where we force Foundation Membership, but users don't legally require that to do certain tasks (CompanyAdmin, Speaker Submissions, etc..) Additionaly, our goal is to create additions to the Members table so we can ingest data from Gerrit (initially) and pull additional data about each user.