added missing `DROP TABLE oc_mail_attachments;` command to the 'Resetting the app' paragraph.

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

Node.js as per https://nodejs.org/static/documents/trademark-policy.pdf#page=3
↵ might be an issue for blind people, (?), but consistent with ← and →
https://portknox.net are inconsistent with their use of big versal k in PortKnox, i reckon if they do it at all, they meant to do it all the time.  ┐('～')┌

In NextCloud 12 I could not find a "Productivity" category. I found the Mail app in Social & Communication

Signed-off-by: Jan-Christoph Borchardt <hey@jancborchardt.net>

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

* Document keyboard shortcuts in README.md

* Update README.md

* Use keyboard markup

Add 	Last modified sorting to link. Thanks to @georgehrke :P

Document was lacking since the feature was implemented.

[skip ci]

[skip ci]

remove version eye badges showing oc mail's outdated dependencies

legacy node doesn't work any more.

based on https://github.com/owncloud/mail/graphs/contributors
and https://github.com/owncloud/mail/graphs/contributors?from=2014-08-03&to=2016-08-02&type=c for the active ones

also drop the table `oc_mail_collected_addresses`.

* log SMTP communication #1392

I copied the thing form imap and changed it. After I try it I noticed it would be better to split the logs. So one for imap and one for smtp.

* additional to my commit form log SMTP communication

Necessary changes for the issue_template that would incur by splitting the horde logs.

* Update issue_template.md

* additional to my commit form log SMTP communication

Necessary changes for the readme that would incur by splitting the horde logs.

the 'owncloud-mail' org was deleted

As discussed with @Gomez on IRC, I created a bountysource org for this app