* XYZ-13: Update Permission and Role structs to new design.
* XYZ-10: Role store.
* XYZ-9/XYZ-44: Roles API endpoints and WebSocket message.
* XYZ-8: Switch server permissions checks to store backed roles.
* XYZ-58: Proper validation of roles where required.
* XYZ-11/XYZ-55: Migration to store backed roles from policy config.
* XYZ-37: Update unit tests to work with database roles.
* XYZ-56: Remove the "guest" role.
* Changes to SetDefaultRolesFromConfig.
* Short-circuit the store if nothing has changed.
* Address first round of review comments.
* Address second round of review comments.
