Make a clean distinction between Debian 7 and Debian 8.  Anticipate the
next Ubuntu LTS release (Xenial) that is planned for support.

resolves #453

Conflicts:
	roles/common/tasks/ufw.yml

(on Debian Jessie, Ubuntu Trusty or older distributions such as
Debian Wheezy and Ubuntu Precise).

Resolves #363.

Addresses #362.

* Postfix: Trusty comes with postgresql 9.3, not 9.1
* owncloud 6.0.1 is part of the distribution, doesn't require opensuse repository
* owncloud requires libapache2-mod-php5
* uses prosody repository that matches the ansible_distribution_release (trusty, wheezy, etc)

String-valued variables containing spaces can be substituted into an ansible
tasks file but they will not be interpreted correctly.

Fixes issue #8. Adds new variable mail_header_privacy, on by default.
Installs postfix-pcre unconditionally, and then copies the pcre file
over and adds the header check to main.cf based on the variable value.
“this header replacement works great, but it logs that the replacement
has been done, which means that you are storing this information,
unless you are anonymizing your logs”

Remove all configuration for MySQL and configure PostgreSQL as the main
database.

All *_mysql_* options have been changed to *_db_* options.

Postgres requires the database user to have a password in order to
connect via localhost. The db_admin_password option is used to set the
password of the admin user (usually postgres).