Rename fields PortfolioInvitation and refactor related sections

[abroddrick]

Issue description

Right now, PortfolioInvitations and UserPortfolioPermissions have two fields that are defined identically, except for their names are slightly different. Not only is this inconsistent and implies they are different from each other more than they really are, it also means we have to have a lot of dupli

Acceptance criteria

• In PortfolioInvitation rename portfolio_additional_permissions and portfolio_roles to be additional_permissions and roles respectively. (This should now match UserPortfolioPermissions)
• Where possible, any html or other files that is checking roles or additional_permissions in both PortfolioInvitation & UserPortfolioPermission should be refactored to remove an redundancy.

Additional context

The two models, note that we want to change PortfolioInvitation to match UserPortfolioPermissions

Links to other issues

• blocked by Manage Profile Page - "Editable" view AND "true read only" view #2789