add fail2ban jails for ownCloud, postfix submission, roundcube, and the Mail-in-a-Box management daemon

(tests squashed into this commit by josh)

closes #840

There hasn't been a sqlite migration yet, since Mail-in-a-Box's creation, but with Roundcube 1.2 there will be.

Dovecot LMTP accepted all mail regardless of whether destination was a user, broken by ae8cd4ef, fixes #852

In the earlier commit, I added a Dovecot userdb lookup. Without a userdb lookup, Dovecot would use the password db for user lookups. With a userdb lookup we can support iterating over users.

But I forgot the WHERE clause in the query, resulting in every incoming message being accepted if the user database contained any users at all. Since the mailbox path template is the same for all users, mail was delivered correctly except that mail that should have been rejected was delivered too.

Added a pre-backup script to complement post-backup script.

adding :
target="_blank"
to 
<li><a href="/admin/munin">Munin Monitoring</a></li> on line 96
Why ?
Because when you click on munin link, and follow links, you lose your index, or click back many times...
So i propose my pull request.
Et voilà ^^

can't change roundcube's default_host setting, partially reverts 6d259a6e

The default_host setting is a part of the internal username key. We can't change that without causing Roundcube to create new internal user accounts.

On some machines localhost is defined as something other than 127.0.0.1, and if we mix "127.0.0.1" and "localhost" then some connections won't be to to the address a service is actually running on.

This was the case with DKIM: It was running on "localhost" but Postfix was connecting to it at 127.0.0.1. (https://discourse.mailinabox.email/t/opendkim-is-not-running-port-8891/1188/12.)

I suppose "localhost" could be an alias to an IPv6 address? We don't really want local services binding on IPv6, so use "127.0.0.1" to be explicit and don't use "localhost" to be sure we get an IPv4 address.

Fixes #797

The emails were not deliverable anyway.

Add SRV to the drop-down to add a custom DNS zone. I made this change on my up-to-date install and it worked without any issues.

The hotfixes were all already applied to master in original PRs. This merge merely brings over the CHANGELOG and the updated install instructions (v0.17b=>v0.17c), including to bootstrap.sh which is what triggers v0.17c being the latest release.

Make control panel login failed messages generic - don't reveal if an email address has an account on the system.