Merge pull request #15 from reneschuster/master

Updated plugins ClamAV, OpenDKIM, Postscreen, RoundcubePlugins and SpamAssassin
Merge pull request #16 from reneschuster/master

Plugin ClamAV, OpenDKIM and SpamAssassin: Small fix
Merge pull request #17 from reneschuster/master

Updated plugins copyright and author informations.
Mailgraph plugin:  Update according new plugin API (0.2.3)
Mailman plugin: Update according new plugin API (0.2.3)
Monitorix plugin: Update according new plugin API (0.2.3)
POP3Fetchmail plugin: Update according new plugin API (0.2.3)
RoundcubePlugins plugin: Update according new plugin API (0.2.3)
SpamAssassin plugin: Update according new plugin API (0.2.3)
Mailgraph plugin: Fix small typo.
Mailman plugin: Fix small typo.
Monitorix plugin: Fix small typo.
POP3Fetchmail plugin: Fix small typo.
RoundcubePlugins plugin: Fix small typo.
SpamAssassin plugin: Fix small typo.