Use debmon repository

Hi,

This feature allow the use of [Debmon repository](http://debmon.org/packages) for Debian 7. You can use it like that:

<pre>
#Install Icinga 2:
class { 'icinga2::server':
  server_db_type => 'pgsql',
  # default to false
  use_debmon => true,
  db_host => 'localhost'
  db_port => '5432'
  db_name => 'icinga2_data'
  db_user => 'icinga2'
  db_password => 'password',
}
</pre>

[Debmon repository](http://debmon.org/packages) is up to date compared to the backports and regularly updated.

Have a good day,

Olivier