Add support for MUC

Receiver JID can be a normal user account or a MUC JID.
Nickname for MUC is by default the sender's user name (first part of JID
before the domain), but can overriden by setting a "nick" variable in xmppnotify.cfg.

set message type to "chat"

some clients (i.e. Sailfish) do not accept message without message type

Refactor commands-xmppnotify.conf.

icinga2 support templates. Use them in
commands-xmppnotify.conf. This makes things a bit more
readable and definitely easier to maintain.

Improve messages

The output of some plugins (and probably some notification
comments) can be multi line. Prefixing only the first by
"Info: " isn't optimal.

Some xmpp clients (notably Conversations) display lines
prefixed by "> " (like in mails) as quotes/citations.
This gives a much better display.

This small tool calls the argument parser with nearly all
possible/needed arguments and shows the resulting message.
This helped a lot in improving messages.

In order to allow easier testing of the argument parser,
refactor its setup into a function. Now we can
"from xmppnotify import build_argparser" and use it.

Missed to remove some spaces in the last commit.
(I never saw notification comments on our system yes...)

Most xmpp clients display messages using a variable width
font. Aligning stuff using spaces doesn't work there.
On mobile clients spaces even add to the message's display
size without adding useful content.

So strip spaces!

{hostname} and {servicename} are the technical/config
names. Get them together on one line and call them "Ref:".
They're references to the config, really.

icinga2 has a "notification type". This is usually
"PROBLEM" or "RECOVERY".

Changed the first line of the message to be like the
Subject of the common notification mails. Especially having
the notification type at the beginning is great for reading
messages on the go ("RECOVERY? Don't even need to read the
remainder NOW").

Basicly removed the "*** monitoring" line. The only
relevant information in it was the monitoringhost.
I could argue that admins probably don't really need that
info at all (the affected host(displayname) should be more
unique, really), but nevertheless re-added the monitoring
host at the end in a smaller line for now.

Move icinga2 command defintions into own file.

* Move the copy for commands*.conf to the other copy
  instructions.
* Reformat the copy instructions a litte.

ConfigDir already contains the /icinga2/ so let's use that.

The command definitions are quite static and do not need to
be changed by the local admin in most cases.
So let's move this to a usable config file.