Merge pull request #11 from reneschuster/master

Plugin RoundcubePlugins: Added new plugins calendar, dkimstatus, logon_p...
Merge pull request #12 from reneschuster/master

Plugin Postscreen: small fix
Merge pull request #13 from reneschuster/master

Plugin RoundcubePlugins: CS fixes
Merge pull request #14 from reneschuster/master

Added SpamAssassin plugin, updated ClamAV, Postscreen and RoundcubePlugins
OpenDKIM plugin: Review
Plugin OpenDKIM: Update according plugin API 0.2.1, changed some functions, updated the README file and added a new config value.
Plugin ClamAV: Update according plugin API 0.2.1, changed some functions, updated the README file.
Plugin Postscreen: Update according plugin API 0.2.1, changed some functions and updated the README file.
Plugin Postscreen: Change SMTP port in Roundcube main.inc.php
Plugin RoundcubePlugins: Update according plugin API 0.2.1, changed some functions and updated the README file.
Plugin SpamAssassin: Update according plugin API 0.2.1, changed some functions, updated the README file and added a new config value.