* adds compatibility for dovecots maildir
* adds role for installing debian backports
* installs newer version of dovecot 2.2.* from debian backports
* in newer versions of dovecot >= 2.2.31 cache index corruption
is fixed
* adds note in README.md
* adds POP3 functionality
* creates testsetup with mariadb,postfix,dovecot,trees
* for further information see vagrant/README.md
* only works with pwhash_algo 0 yet
* see limitations in vagrant/README.md