This singleton provides access to all the plugins in the Kettle universe.
It allows you to register types and plugins, query plugin lists per category, list plugins per type, etc.
This interface describes a plugin type.
It expresses the ID and the name of the plugin type.
Then it also explains what the plugin meta class is called and classes the plugin interface itself.
It also explains us where to load plugins of this type.
putRow is used to copy a row, to the alternate rowset(s) This should get priority over everything else!
(synchronized) If distribute is true, a row is copied only once to the output rowsets, otherwise copies are sent
to each rowset!