Bug 34619: Show debug mode column in list of SMTP servers

Bug 34619: Show debug mode column in list of SMTP servers

This patch adds a column to the table of SMTP servers which shows
whether debug mode is on or off. This information was previously only
conveyed through the color of the text in the table row.

To test, apply the patch and go to Administration -> SMTP servers.

- If necessary, add one or more SMTP servers so that there are more than
  one: At least one with debug mode on, at least one with debug mode
  off.
- In the table listing SMTP servers you should see a column for "Debug
  mode," where the rows indicate "On" or "Off."
- Each row which is highlighted in red should show "On" for debug mode.

Signed-off-by: Émily-Rose Francoeur <emily-rose.francoeur@inLibro.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>