Disambiguate sent and created

At the moment we say that you either ‘add’ an alert or ‘send’ it.

This is confusing because:
- an alert isn’t received on people’s phones until it’s approved, so
  this is really when it is ‘sent’ conceptually
- an alert can be rejected before anyone receives it, so the UI can say
  an alert that no-one ever received was sent

This commit re-labels things so that the the first part of the process
is ‘creating’ the alert.

This makes all the permissions nice and distinct from each other. Adding
templates and adding alerts feel conceptually quite different things
(what are you adding the alert to?).

app/main/forms.py

@@ -1031,7 +1031,7 @@ class BroadcastPermissionsForm(BasePermissionsForm):
         ],
         filters=[filter_by_broadcast_permissions],
         param_extensions={
-            "hint": {"text": "Team members with permission to add alerts or approve alerts can also reject them."}
+            "hint": {"text": "Team members who can create or approve alerts can also reject them."}
         }
     )