Move Categories related classes to subdir.
Move CSS lexer/parser to css/ subdir.
Move enum processing out of Aggregator.
Move Accessors processing out of Aggregator.
Move Ext4 events processing to Ext4Events class.
Move overrides processing out of Aggregator.

In BatchParser use the Aggregator#classes to retrieve the result
instad of the old #result method.  The latter is now used only in
testsuite.
Extract class for removal of ignored classes.
Rename Accessors#create_all! to #process_all!.

To unify the naming with other classes doing similar stuff.