Feature: Introduce Super Admins (#705)

* Feature: Introduce Super Admins

- added new devise model for super user
- added administrate gem
- sample dashboards for users and accounts

Co-authored-by: Pranav Raj Sreepuram <pranavrajs@gmail.com>

app/javascript/dashboard/assets/scss/super_admin/index.scss

@@ -0,0 +1,5 @@
+@import '../variables';
+
+.superadmin-body {
+  background: $color-background;
+}