Merge branch 'improve_notification_mails' into 'master'

Improve notification mails

The mail subject line is too long for some mail clients,
so i removed the $NOTIFICATIONTYPE$ variable from it,
because it is not needed to understand the problem/recovery.

This is an example of a mail send out using this change:

    Subject: WARNING - aardwolf: APT

    ***** Nagios *****

    Notification Type: PROBLEM

    Host:      aardwolf.unstable.bitmask.i (aardwolf)
    Address:   199.119.112.205

    Service:   APT
    State:     WARNING
    Duration:  0d 0h 13m 5s

    Date/Time: Fri Jan 15 10:04:55 UTC 2016

    Output:    WARN - APT WARNING: 20 packages available for upgrade (0 critical updates).

Before it looked like this:

    Subject: ** PROBLEM Service Alert: aardwolf/APT is WARNING **

    ***** Nagios *****

    Notification Type: PROBLEM

    Service: APT
    Host: aardwolf
    Address: 199.119.112.205
    State: WARNING

    Date/Time: Thu Mar 10 21:57:23 UTC 2016

    Additional Info:

    WARN - APT WARNING: 1 packages available for upgrade (0 critical updates).

See merge request !22

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