admin: Align auth_providers/groups with resources
Split the auth_providers.py and groups.py to four different categories: views, filters, actions, utils. This split aligns these files with the rest of the resources in the `resources` folder. Note that due to the simplicity of these resources, the actions, filters and utils files are left blank.
snf-admin-app/synnefo_admin/admin/resources/auth_providers.py → snf-admin-app/synnefo_admin/admin/resources/auth_providers/views.py
snf-admin-app/synnefo_admin/admin/resources/groups.py → snf-admin-app/synnefo_admin/admin/resources/groups/views.py