Account deletion (#3728)

* Add form for account deletion

* If avatar or header are gone from source, remove them

* Add option to have SuspendAccountService remove user record, add tests

* Exclude suspended accounts from search

app/javascript/styles/forms.scss

@@ -303,7 +303,10 @@ code {
       font-weight: 500;
     }
   }
+}
 
+.simple_form,
+.table-form {
   .warning {
     max-width: 400px;
     box-sizing: border-box;