listfilterplugin is an simple example of making a filtering QMailContentManagerPlugin. 

If an incoming message, that comes from a mailing list (as identified by QMailMessageMetaData::listId()) is automatically
moved into a folder that contains the same name (if it exists).

e.g. If you have a folder dev@meego.com and an email with listId of 'dev@meego.com' comes in, it'll automatically get moved. 

This example is NOT built by default, to avoid it accidentally getting deployed.
