Add app_id to roles schema

[nelsonic]

In order to make RBAC useful we need to be able to create roles for Apps.
And when a new person joins an App, they need to be assigned a role specific to that App.

Todo

• Add app_id field to roles schema.
• Request to /approles/:client_id should return the list of roles as JSON
  where :client_id is the first half of the AUTH_API_KEY (similar to how auth_plug handles auth).
• List of Roles for an App should include both the app-specific roles
  and "default" roles created by seeds.exs Get List of Roles for App  #110
• Add app_id to conn.assigns.person so that we know which app the person authenticated with. Related: https://github.com/dwyl/auth_plug/issues/24

[nelsonic]

At present the roles listing looks like this: http://localhost:4000/roles

Next: add app_id to the table. ⏳

[nelsonic]

A non-admin can create a new role for their own App(s):

Person with superadmin role can create a role for any/all Apps:

Chrome does not allow me to take a screenshot of the whole screen with the select showing all the options so here is the separate screenshot showing all the apps:

[nelsonic]

Roles as viewed by Admin: http://localhost:4000/roles (showing two custom roles)

[nelsonic]

Marginally better layout: http://localhost:4000/roles/1/edit

[nelsonic]

Added app_id to conn.assigns.person ✅