Moved mail message sender something down

Closes no issue

What does this MR do?

When you reply to mails, the send button is back, but the sender is now missing. This MR moved the mail sender something down.

How confident are you it won't break things if deployed?

(be honest!)

Links to related issues

!1127 (merged) https://yunity.slack.com/archives/C74JC2V26/p1580340709045900

How to test

Steps a reviewer can take to verify that this MR does what it says it does e.g.

1. Checkout branch locally
2. Import sql INSERT INTO `fs_mailbox_message` (`id`, `mailbox_id`, `folder`, `sender`, `to`, `subject`, `body`, `body_html`, `time`, `attach`, `read`, `answer`) VALUES (102410, 19708, 2, '{\"host\":\"foodsharing.network\",\"mailbox\":\"region-341\",\"personal\":\"Foodsharing Anmeldevorgang Quiz\"}', '[{\"personal\":\"b.menzel@foodsharing.network\",\"mailbox\":\"b.menzel\",\"host\":\"foodsharing.network\"}]', 'selfmail1', 'selfmail1-1', 'selfmail1-1', '2019-10-16 21:58:46', '', 1, 0);
3. Login as store manager or amb (bot)
4. Than is the mail visible on dashboard. The message can be open only over the dashboard.
5. Click the button "Antworten" in the message
6. Insert a long text until scrolling is available.
7. Is the mail sender showing?

Screenshots (if applicable)

https://files.slack.com/files-pri/T0B6WCFM5-FTCDULYSJ/unbenannt.png

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, merge request link, username(s))
• Once your MR has been merged, you are responsible to update the #foodsharing-beta Slack channel about what has been changed here. They will test your work in different browsers, roles or other settings