Preliminary solution to issue #19

Introduces a plugin to save information on particles of few selected types after parton shower. It supercedes the FlavourAnalyser plugin, which is removed. The new plugin is still to be debugged and commented.
Added fillDescription method to PartonShowerOutcome plugin
Added documentation for PartonShowerOutcome. This fixes #19

With RelVal ttbar datasets this plugin in default configuration adds about 50 bytes per event, which is 7%.