DEV: Correct typos and spelling mistakes (#12812)

Over the years we accrued many spelling mistakes in the code base. 

This PR attempts to fix spelling mistakes and typos in all areas of the code that are extremely safe to change 

- comments
- test descriptions
- other low risk areas

lib/tasks/admin.rake

@@ -39,7 +39,7 @@ task "admin:create" => :environment do
     email = ask("Email:  ")
     existing_user = User.find_by_email(email)
 
-    # check if user account already exixts
+    # check if user account already exists
     if existing_user
       # user already exists, ask for password reset
       admin = existing_user