app: do not show drafts in preview

[redshiftzero]

Description

Fixes #997. The previews should show activity from the server only (cc @ninavizz), that is successful replies, and activity from the source.

Test Plan

0. Add to below this line in the server endpoint:

+            early_fail = random.choice([True, False])
+            if early_fail:
+                abort(404)

1. Submit replies until one fails.
2. Verify that the preview snippet does not contain the text of the failed reply.

Checklist

If these changes modify code paths involving cryptography, the opening of files in VMs or network (via the RPC service) traffic, Qubes testing in the staging environment is required. For fine tuning of the graphical user interface, testing in any environment in Qubes is required. Please check as applicable:

• I have tested these changes in the appropriate Qubes environment
• I do not have an appropriate Qubes OS workstation set up (the reviewer will need to test these changes)
• These changes should not need testing in Qubes

If these changes add or remove files other than client code, packaging logic (e.g., the AppArmor profile) may need to be updated. Please check as applicable:

• I have submitted a separate PR to the packaging repo
• No update to the packaging logic (e.g., AppArmor profile) is required for these changes
• I don't know and would appreciate guidance

[sssoleileraaa]

lgtm, failed replies no longer show up in the preview. also tested that draft replies no longer show up there.

[sssoleileraaa]

nice solution 👍