Add ability to have settings sent to preprocessor

Currently a plugin can get configuration settings from the init.properties through the sess-man/plugins-conf/[plugin id] node but this is only available to the process() method of the plugin. The preprocess / postprocess methods could benefit from custom settings as well.

As a first step being able to pass the settings along to those methods would be great. A further step would be to allow for some init call that would pass in the settings. One reason I see for this is that if you have a plugin interacting with both preprocess and process steps of a packet it is hard to know which one should initialize the plugin unless you have a custom state property on the plugin class to see when it was initialized (lazy loading). Would be nice to have that init happen when the class is first instantiated.