Use core Organization model with ROR data for supporter identity

[joemull]

We are in the process of implementing ROR more fully in the core of Janeway. Once that is complete, we should update the Supporter model in this plugin to use core.models.Organization for the identity of Supporters, and just maintain the Supporter model in this plugin for support-related things. Then we should update interfaces where supporters are added or searched so they draw on the Organization name data. Places like the Manager, the Signup page, the Recommend Us page, and All Supporters list.