Improve user role and site management

[SlimDeluxe]

User role and site management should be improved.
In Eclipse, which is a multi-tenant app, sites equal tenants. When a user is assigned a role for a site, he becomes "active" on that site.
By default, all new users should get the panel_user role. When the user is stripped of all roles, he cannot use or log in on that site.

Role create/edit:

• Set role as global or site-specific (when editing or creating role)

User create/edit/view:

• Set user's global roles (when editing or creating user)
• Set user's roles for each site
• When saved, the site_has_user table should also be updated
• View user's global and site roles on the view page (only for sites the admin has access to)

User control:

• User can login only on his sites
• New users must get the panel_user role, no matter where they came from (registration, seeder...)

Site management:

• When a new site is created, all users with global roles should be added to it, so they have the role on the new site also

User list:

• By default, the users list should display only users for the current site
• Add columns for user's global and (current) site roles
• A filter can be set to see users from all sites (that the admin has the access to)
• A filter for global and site roles (any role/specific role)

All features must have an accompanying feature test and, if needed, unit tests (for uncovered edge cases).