Fix travis build by fixing ansible-lint version

Before sudo rule merge
https://github.com/willthames/ansible-lint/pull/96

* Add test-requirements.txt
* travis: enable cache for pip packages

Set opendmarc password in testing.

Remove LetsEncrypt checklist item

LetsEncrypt support is not yet on master.

Fix links to Ansible website in readme

Adding monit tunnel information to Readme

Updated contribution guidelines

Added "UseRoaming no" to ssh.config to fix OpenSSH: client bugs CVE-2…

see: http://undeadly.org/cgi?action=article&sid=2016011414

ufw tasks shall have the ufw tag

resolves #453

Writing clarifies thinking and leaves behind guidance for future
maintainers.  Design descriptions shouldn't be required, though,
especially for trivial modules.

Users expect role authors to make decisions.  The role author is
supposed to be the expert who knows what choices to make on behalf of
the user.

I probably got this wrong, but I'm putting a stake in the ground based
on work I've done on the Roundcube module and adding Let's Encrypt
support to the common module.

sl: properly install changed certificate and restart apache on changes

Pin Selfoss version to an actual release

Generate 2048 DH group and add it to Postfix

update openvpn server config

Change default network buffer size
Should increase tcp tunnel speed for openvpn < 2.3.9
https://community.openvpn.net/openvpn/ticket/461

Configure logrotate permissions for selfoss

Remove reference to Google's DNS servers

Per discussion on #429 (after the merge). This project is about encouraging users to run services themselves and not rely on for-profit corporations such as Google.

Add SSL stapling cache for distributions with Apache 2.4+

Fixes #406

Closes #429

add additional comment about `tun-mtu` parameter in openvpn config template

- google dns setting for client
- verb level
- mtu
- TLS settings

Notes about security: https://blog.g3rt.nl/openvpn-security-tips.html
Check privacy: http://witch.valdikss.org.ru/

change auth to internal_hashed

Use common_timezone and fix idempotence